Doing AOS- rear intake plenum boot - how on earth to remove?

So I am down to the last couple steps to removing the LH intake manifold to access the AOS on my 99 C2, but I am having a heck of a time moving that rear intake plenum boot. I have all the hose clamps completely loosened but that boot is so rigid it is resisting any efforts to either slightly compress it to move it, or push/pull from one side to move it the rest of the way. The front ones were a piece of cake compared to this. Any tips on how to move that thing?

You need to remove the left intake manifold bolts and lift up the left manifold first. That rear plenum is not designed to be removed without loosenng the left (or right) intake manifold first.

Well, that would explain it. I was about to do that because that seemed the easiest way but the Pelican how-to guide I was following said to do that after. Also, my 6 bolt heads for the intake appear to just be standard heads and not torx like the guide mentions. I presume just another typo?

The Pelican guides and photos are good reference but sometimes they may not be completely accurate. Also, they did the procedure on a specific model so sometimes there are natural variations too. Regular hex bolts are correct.

Also lower the engine about 3" (almost to the cross brace) to give yourself more room to work.

I've loosened the bottom bolts on the motor mounts and really didn't notice much difference in motor height. Is there something else I should loosen to lower it a bit? e: Just to be clear, I have 5 of the 6 bolts out right now but I can tell that rear one is going to be a royal PITA. Even if I get it out, I need to get it back in when I'm done LOL and I can see any height I can get in the back being a big benefit.

You may have to remove the motor mount nuts and support your engine with your jack, then just ease it down. Some people us a block of wood between their jack and engine but my jack has a rubber pad on the top and seems to work better without a block.

So just to make sure I understand you, you think I should pull the mount nuts right off? How far can I let the motor drop before it starts stressing out the front/transaxle mount? I am familiar with the procedure of supporting the motor with a jack (I replaced the mounts before) but I am a little leery of taking the motor right away from them and letting it drop (albeit supported) but if that is the procedure and it won't hurt anything, I'll try it. How far can I let it drop away from the bottom stud of that mount? I am truly stuck at that back bolt for the intake manifold - that's literally holding everything up with me right now and it has to come out.

What year is your engine? You need to remove the engine mount bolts and lower the engine to the max till the trans touches the cross beam support. Just make sure you release the tension on the power steering hoses, fuel line (may heed to disconnect), and O2 sensor wires (may need to disconnect them). You won't hurt the trans mount btw.

It's a 99 C2. I assume the PS lines would be near the AC? (I already unbolted the AC compressor as I'm doing the RH cam chain tensioner and battery cable). Where would the fuel lines be? I've never lowered the motor before so this is sort of news for me. I presume the o2 wires will be easy to find BTW, thanks for the help guys, really appreciate it.

Good points Ahsai. On my '99's (same as OP) I could get it down almost to the cross brace without stressing anything but the O2 sensors wires. And simply removing the wires from the support clips provided enough relief. One note though, if you have a DOF (not sure why anyone would but my track car came with it) you will have to remove the rear sway bar to lower the engine without damaging the DOF. The first AOS I did, I was also doing the water pump so o had the coolant drained and was able to unhook the coolant hoses which provided a lot more room along the drivers side of the engine compartment by allowing me to move everything over to the right. The second time I swapped an AOS, I tried without moving the coolant lines and had no success. So I drained the coolant (you can reuse it) moved the lines and things went much smoother. By the way, this little doo hickey is one of my favorite Ahsai tips. It's a filter that goes over a 5 gallon bucket and allows you to strain your fluids before reusing them. Works with oil as well. 5 Gallon EZ Strainer Insert 55 Micron for Bucket Pail Filtering Water Paint Biodiesel WVO WMO Vegetable Oil https://www.amazon.com/dp/B00QSLNLJC..._1OSayb8AGB5VD

I drained about 2L of coolant when taking the alternator out (I just removed the braket which opened the cooling system) and I might just drain it all as per your suggestion. Since I have no idea when the coolant was last replaced I'll probably just replace it all instead of re-using. What is a DOF?

For that last bolt (closest to the AOS) on the left intake manifold, you need to do two things 1) lower the engine enough to get your hand from above. Use a 1/4" drive ratchet, an extension and a socket 2) loosen the AOS and push it up a bit. Otherwise it will block that bolt Coincidentally I just replaced my AOS ('03 3.6L so it's a bit different and even more difficult due to the rearmost bolt on the AOS) while my trans is out. I was able to do everthing from the bottom but it's still not easy due to that rearmost bolt on the AOS.

Direct Oil Feed. Some concept where you remove the outer seal of the IMS and pump oil directly to it. It's a little less invasive on mine since the engine was replaced in '06 with a factory crate engine that had the updated larger single row IMS. Still though, it's not something I would have added.

This photo of mine, 99 C2, might help you understand where you are headed with the rearmost intake bolt. As said, without dropping the engine down I just do not know how you would get to that bolt, and it is still a royal PITA to remove. Remember the intake bolts have loctite on them so it is a long, slow removal process. Also, getting that rearmost bolt back in is almost as impossible. I used some painter tape to hold the bolt in a socket and extension in order to get it set in place, then a bunch of swivels and extensions to tighten over the top of the intake manifold. Once you get the last intake bolt out, you slide the intake manifold to the left and away from the rear plenum. My AOS has already been removed and picture was taken before a major cleanup in there.

Yeah, that bolt is a PITA for me as well. Both the AOS and a wire bundle are right on top of it, blocking any tools.

Thanks very much for the replies guys. I haven't worked on it the last couple days but will drop it next chance I can. I got the other 5 bolts out easy enough and looking forward to yarding that intake out.

So started on this again today. (I only work on it a couple hours a weekend so it's a slow project!) I dropped the motor off the back mounts and certainly has given me some more room - thanks guys. These to hoses are being a royal PITA today and stopping me from getting a socket or a stubby wrech on that bolt. COfh54R.jpg I presume these are fuel lines. Do you guys pull these off to get at them or go about it another way? If I do move them do the hoses just come right off the steel lines? Should I be doing something else? It's a little frustrating because I am sooo close e: Just looked closer at your photo Ashai - is there a bolt in that hole to the left of your red square? I'm just kind of feeling around in the back and that might be what I am feeling. Man, it's even tougher than I thought if so!

Hang in there. It takes a lot of patience. That was not my picture but I have the same holes. That hole that's left of the difficult intake manifold bolt is for a nylon cable tie, no bolt goes through that hole. You may have to do everything by feel. I did.

I hear ya, everything for that sucker has been by feel until now. I actually think I'm going to try getting at it from the right hand side and remove that top rad hose that is in your photo. I have the alternator out so it's very open on that side. I already emptied out the coolant top-side of the motor and would give me an "almost" straight shot at the bolt other than the top of the AOS being in the way but at least it's visible on that side which is a plus! But now I am hung up by a friggen PITA hose clamp! Even completely opened it's still too big to slide up. Grrrrrrr!

Have you tried pushing the AOS straight up for an inch or so? Then you should have a straight shot of that bolt from the top (by feel).

No, not yet but thanks for the tip. I have removed the 2 mounting bolts but since I've never done it before I wasn't sure how much I can get away with moving/jostling things. I think I'm going to try taking out that hose tomorrow and work that angle. It's really a fairly straight shot at it from there and I think will make it easier to start the bolt for the re-install. Did you guys re-loctite those intake bolts or just torque up as-is?

I just reused the old bolts and torqed them to spec. No loctite used.

When you manage to get the last bolt a little bit loose, you can pivot the manifold a little bit to the left and get the rear plenum unattached. Then you can pivot the intake manifold to the right and gain a little better access to the rear bolt. Make sure to have a magnetic socket or a magnet in there to catch that bolt. Since you are working blind, you don't know when it finally comes out and it is easy to drop. Took me two days to find that bolt! Also remember that there are intake manifold gaskets (oval O-rings), so when you finally get it out make sure all three are still on the manifold. Otherwise, they dropped into one of the intakes and you will need to fish it out.

You are almost there. No reason you shouldn't be able to get the bolt from above with a 1/4 ratchet, extension and U-joint. It only took me an hour to find the bolt I dropped. Went up through the wheel well IIRC. Total pain but not tragic.

This is a fascinating thread......... great reading.

Got you, you rat bastard 7AfifUY.jpg The prize is now easily in sight kWdPzQL.jpg I had Mrs. Spud72 holding my flexible magnet in off the socket as I pulled it off in case it fell, just as you guys mentioned. After I pulled the intake she looked at me, mouth slightly agape at the underhood condition of our Porsche. She said "Don't you die until you get this fixed and out of the garage!"

I like Mrs Spud. Congrats!! Changing your AOS is almost a DIY "right of passage" on these. You have a few hurdles left but just stay after it. You are almost halfway there!

She's a sweetheart, really. Hey it looks like there are pinch-style clamps on a couple of those lines off the AOS. Do you guys just cut those off and replace with standard clamps? I haven't run across those yet until now and would rather avoid cursing and swearing for several hours on a couple of stupid clamps.

I usually don't reuse those spring style clamps, especially if they are so difficult to access if they cause a leak. They tend to loose their strength with age. I would replace those with new identical ones or just the worm type.

Will do. For removing those pinch clamps though, do you just cut them or get through the "hole" and pry them apart? OH, almost forgot, I found for that back bolt once I got the motor dropped darn near to the cross member, I was able to get that bolt with the 1/4" extensions (2 of them) but with the universal I just couldn't get enough torque on it to break free. I was able to just fit the ratchet straight on the extensions and finally broke it free after several curse words. So, if a guy takes your time and lines it up, you can do it without a universal! Shocked me, to be honest.

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That's what my post #13 said, rachet with extension and socket I use this type of pliers for those spring hoses https://www.amazon.com/OTC-4525-Cabl.../dp/B000F5JM0O You can try to use those needle nose vise grip pliers too.

I've got one of those but these clamps don't look like the spring type. I'll try and take a photo to explain.

My fault. I thought I had used a universal.

They look kind of like this. Did you guys have a couple of these on your AOS too?

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Oteiker clamps! Yeah, either cut with a dike at the ear or pry on the ear to make the ear loose and the whole clamp will loose tension.

You sonofa()&%#@ Got it. yEFVv7S.jpg Finally. What a royal pain. The final insult was after I had it exposed 2 of the hose clamps were those pinch-type and the eye to wedge open was in the most awkward position possible. Then squeeze connect on the big bottom left hose refused to budge. Took me darn near 2 hours just to free it. Finally after loosening everything else I was able to wiggle it enough to break it loose. Then, as I was pulling the AOS out 1 of the hose clamps fell off and I don't know where. I have to find it - crankcase had an open port and if it fell in there I am having a bad day. The good news is I put my snake camera over it and don't see it in there - so that's a good sign - but I will not be able to sleep if I put this thing back together without finding it. Hopefully in the daylight tomorrow I will be able to snag it, then start on re-assembly.

I bet the next time you do a job like this (will there be a next time?) you'll stuff some rags in those open ports... Good luck finding that clamp

You can see from my earlier picture the rags stuffed in the intakes. Did that prior to pulling out the AOS. Also covered it with towels just to make sure. The damn thing is - I almost screwed up. After getting the new AOS back in, I sat there and did several trial fits of the intake manifold, then decided I was ready to go, put the intake manifold in place, worked it back into the rear plenum...and then duh!! Pull back out and take the rags stuffed into the intakes out. Sheesh! Go slow and think it through every step of the way. You are almost there. And yes, find that clamp. Maybe a magnet down the intakes. Also find the IPhone is invaluable for taking snapshots of hard to reach/see places. Maybe a straight shot picture down the intakes would help you find it.

Oh I had the ports covered, the one I am concerned about with the crankcase is actually what the AOS itself was mounted on and became exposed as I pulled it out. Tough to cover it ahead of time as I am removing it I am pretty confident it's not there though, I had to manipulate the AOS pretty heavily in removing it so that clamp is probably anywhere but around there. I am optimistic I'll find it in the better light though. I hope!

Any of you guys know the torque spec for the 2 AOS bolts? Can't find in my Bentley book.

7.5ftlb if it's an M6. I just wing it though.

Yeah I'll go by feel. Thanks man. Reassembly has begun.

So just an update on the status of the mysterious missing pinch clamp... I literally looked over the entire block/head/sides of the engine and engine compartment and couldn't find the clamp both by eye and with help of my snake cam in areas I couldn't easily see. I stuck the camera into the AOS crankcase opening even further and no sign of the clip. I removed the rags from the intake and stuck the camera in all the way to the valves if somehow by fluke it made its way past. Nothing. I spent probably over 3 hours doing this yesterday. I took the old AOS and checked the orientation of the port from which the clamp that would have been missing. It was then that I had an epiphany that it was readily accessible... in fact so readily accessible and I wouldn't have left it on. I also had a shadow of a memory of holding a mangled clamp in my hand after bending it loose. I then realized that I am almost certain I pulled it off when I loosened it and just immediately threw it away. Of course garbage day was yesterday so I couldn't rummage through the can to be positive but I do remember holding a clamp like that and it is the only one it could be since there was only 2 clamps and I still have one. So to be extra safe, I replaced the old AOS to its original installed position and went through the motions of removing it to see where it could have possibly fallen if by off chance it was still on There is no way it would have fallen backwards into the AOS port that would have become exposed as I removed it - it was just too far away and behind and it wouldn't have fallen in some place that I haven't looked over with a fine tooth comb. So I am satisfied with any real degree of uncertainty that the clamp is not posing a danger and almost certainly thrown away. As such I have begun to clean up the dirt/leaves/debris on top of the motor and start the reassembly process. Yay, half way through the job! Next steps: Vacuuming/Cleaning the topside of the motor Replacing and buttoning in the new AOS Replacing the alternator/starter/jump point cable Replacing top right cam chain tensioner, conveniently located under the AC compressor fin!

I think I am going to have to spring for my Indy to do this job when the time comes. It seems a bit more complicated than changing my cabin air filter.

Good god, I'm so dreading this one when it comes. I tried get my indy to do this preemptively while the engine was out...he declined. Great job OP

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"Hey, uh, while you're there, how about - " "Nope. Not gonna do it." "You don't even know what I - " "AOS. Not gonna do it."

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Not going to lie, it's not super easy like an oil filter change but if you'd be comfortable changing an alternator, starter or thermostat you could probably do this if you take your time. Don't understand an indy not doing it if the motor is already out though- that is just so weird. It would probably be a 10 minute job with everything accessible. The hardest thing by far is just working with the cramped quarters. Thanks for the congrats, but it's premature at this point! I'll probably screw up doing my other work and either start the car on fire or throw the timing chain LOL E: Forgot a few steps! To do list (in rough order): Clean top of motor Finish AOS install Replace alt-starter-jump point cable Replace RH timing tensioner Re-bearing belt idlers (Pretty sure they are original right now - IIRC just standard 6202 bearings so I grabbed some nice SKF ones from the shop to throw in there) Clean the throttle body Re&re and clean the idle air valve FIN!!!~~!

Yah, I'm going to guess it's because he has a fat backlog, and my car gave him some unexpected difficulties and pushed back his schedule even more. He was feeling the pressure from other customers. So he just said eff it because the AOS readings were fine. He was polite about it and I could have pushed back. I was just being lazy, I'll save money by doing it myself.

So I am buttoning everything back up and just about to call it a day as my flashlight is running low on charge, but I have a mystery plug I need to figure out where it goes. It's on the same harness as the idle control valve and throttle position sensor (right off the throttle body) but it's on a lead about 12" long, which puts it in the vicinity of the PS pump and AC compressor, but I don't really see any plugs that mate with it.. at least not readily visible. It could go on the alternator side, but I know I have the alternator plugged in. Ideas? I am not desperate yet but if someone knows off the top of their head that would be awesome.

Air flow sensor in the filter box?

Plugs into the thing (I forget what that is..evap purge valve?) over and on top of the alternator, to the left of the TB

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Nope, not that. I have that one done. Looks like exact same style of plug though so easy to make the mistake. Pretty sure it's the RH side of the motor. If I understand you right, that's got its own lead from the RH side.. different shape too. I don't think it would reach anyhow, unless I am just misunderstanding you? I'll just have to take a better look, I ran out of time yesterday. That AC compressor keeps getting in the way and is a pain in the butt. OH, meant to ask, you guys that have pulled that compressor, are you able to get that rear bolt out? I can't do it without opening the high-pressure line and I certainly am not going to do that. The rear bolt head just is in the perfect position to hit that steel line.

Since I made a mistake on mine while buttoning things up....the left side rubber ring of the front plenum has the vacuum port on it. I forgot to connect the hard plastic vacuum line back into that and the car ran like crap until I backtracked and found it disconnected. Thought I had done something wrong in all that work, but just turned out to be that.

Hmmm...I just went out and looked at mine. The three bundles of wires under the TB, one connects to the ICV, one to the TPS (both on the TB) and one goes to the evap purge valve. I did not see any wire bundle going over to the right. However, I cannot see the backside of the AC compressor. Did you undo that for some reason? Definitely not the one for the MAF sensor on the air filter box. From your picture, I'm not seeing the wire connector to the ICV on the TB...and chance you missed that one?

There's no such injector/valve type connector on the right side of the throttle body in that area as far as I remember. There's the engine compartment temp sensor on top of the right intake manifold but I don't remember if it uses this type of connector.

I know this is kind of a goofy picture, but it does show the three wire bundle under the TB. The orange seal one plugs into the throttle position sensor, the square one plugs into the Idle Control Valve on the throttle body, and the third one goes over to the evap purge valve.

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You were absolutely correct - that's what I get for not reading your post properly. I had decided in my mind you meant the one to the left of the alternator - not the one on top which is exactly as you described it. I thought the one in red, you obviously meant the one in blue and that is it. Thanks! Also, champ job on detailing your engine man. You should do a post about that!

LOL. Thanks. 99 C2 w/138K miles. Anyway, I really need to find a way to circle and point to things in my pictures. Good job and I hope it is warming up for a test run very soon.

Oh, and one other anomaly I have had with the TB cable (having removed that several times), finished up the whole job and started. Really fast idle...like 1200-1300 RPM. I found that the throttle cable was holding open and was not allowing a full return to idle position. Undid the throttle cable and pulled it. The backside of the throttle cable "snapped" into the little black plastic holder on the TB and that was it. When you're tired, you miss stuff.

I was pretty **** with putting the throttle cable back in place before I snapped it in, it's angled in the same way as your photo and the butterfly on the TB is indeed closed, so hopefully i have it. Thanks for the reminder though. Oh gosh, the weather has been so nice even up here in Canadaland it's been killing me not driving it. Every day has been pushing 20C, sometimes warmer. I think I've got about one or two hours of work left until it's all buttoned up and begin refilling the cooling system... which, btw, any tricks I should know about for that? Is it a crazy idea to keep its *** on stands to try to keep the rear a little higher for the air to come out? Edit: Also, the bearings in the idlers are 3202, not 6202. I wasn't able to measure the width well until I pulled them. A really PITA to remove though, needed a press.

Yes, it is a good idea to keep the rear end up when filling the coolant system. I know others highly recommend the ULift vacuum filler system. But on the times when I have had to drain the coolant just on the engine side, slightly overfill the coolant tank, leave the coolant cap off, run the engine until it is slightly warm (less than five minutes), it will burp out some air and the coolant level will drop in the tank, refill to the max line, install cap and put the bleeder valve in the up position. Short drive to warm it up all the way (thermostat open) and then home. You want to be very careful on the short drive, i.e., short by meaning just until it gets to operating temp and no high RPM's. Our engines are very sensitive to hot spots in the heads and you do not want to stress the engine at all. Cool down, remove coolant cap and refill in between the max/min line. You may have to do this a couple of times. Watch the level over several drives and you should be good to go. If I were doing the idler pulleys, I think I would just fork over the money for a whole new set. But that's just me.

Normally I would absolutely agree, but I took a look at it and saw how easy the bearing should pop out I thought it would be a waste to replace the whole thing, so I never bothered ordering any. Then I went to replace it, holy smokes. I'm ordering a couple next time I do a parts order

Well, at around 21:30 the never ending Project, let's do an AOS, RH timing chain tensioner and alternator/starter cable on the 996 came to an end. Finished installing and double checked everything (god, that AC Compressor was almost as much of a pain as the AOS itself), dumped in some coolant and PS fluid, held my breath and turned the key. 9aDbnSh.jpg Roared to life instantly and no warning lights. After a few minutes settled to a smooth idle. Let it warm up, took it for a rip. No stumbles, hesitations, shuddering, nothing. Only thing at all were some smells that I am sure just the coolant and PS fluid roasting on the block. Going to make sure there are no leaks as it sits overnight, but other than that go through torque a couple things down and DONE ueDCHGN.jpg xBUyvrQ.jpg First time it's been on the road for about 2 months (due to my only working on it an hour here and there) and it felt great. I would like to thank all those guys that helped out with some tips and tricks. I hope to pass it along going forward!

Well done and enjoy it in good health!

Thanks, although Mrs. Spuds criteria of "getting it together and out of the garage before I die" is now met, I am a little concerned!

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Haha, I could hear her disappointment in your video when checking the fuel presaure All is good now though.

Don't think the fuel pressure vid was mine but she told me this AM that I am not in imminent danger!

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Sorry, I got mixed up. I was thinking about Jackstand's vids on another thread. Glad to hear you're not in imminent danger

Lol, she's a Colombian princess....had never been that close to a starting engine. An assault on the senses. The pressure reading meant nothing to her. good videographer though. I've read several procedures for AOS change, all very similar. I'm wondering two things....1) possible to do from below, lowering engine as during water pump change? When I repaired a leaking AOS clamp from below I checked access and it was tight but accessible and, 2) with all the effort a few more hoses, cables, and fasteners one could drop the engine/transmission and knock out several projects while there. It looks like about 4-5 hours of labor additional to drop the drive train and more fluids but great access for maintenance/upgrades. Looks like you could suspend the a/c compressor and not lose the charge. Thoughts?

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Good to have the wives helping so they will appreciate the challenges I can confirm with the tranny removed, you can work from the bottom alone and not touch anything above. The other way is like you said during water pump change you lower the engine as much as you can and work from both the top and the bottom. You still have to remove the left intake manifold though. ​​​​​​Yeah, dropping the engine is not that much longer. I don't think I will drop the engine just for the AOS but if you need to replace the ims and clutch, definitely drop the engine.

Having recently done all of this stuff, I would definitely +1 on dropping the engine if you have 2 or 3 tasks, one of which is AOS (or coolant tank!). Especially if you are due to flush the coolant anyway.

I've never dropped the engine completely yet, but I concur. If I had to do this and one other hard to get at thing and if dropping the engine made both super easy? Yeah, I'd probably drop the engine too.

That rear plenum is a major pain in the rear, but it can be removed and put back in without loosening an intake manifold. To remove, remove the hose clamps. If the hose clamps are pointed in a way that you can't loosen them, then you'll have to cut them off and replace them. Once the hose clamps are off, you can use a pry bar to move the boot as far to the side as possible working either side. Eventually it will come off. Putting it back on, you have to put the boot on the left side completely over until the edge of the boot is inline with the intake. Its not easy to do, but it can be done. Then the right boot front edge has to be put on as far as possible with the front of boots' edge lined up with the edge of the intake. Then you have to carefully manuver the left side of the plenum on while getting the right side started. Eventually you'll get it to pop into a position where you can lever the boots onto the plenum and put the hose clamps on. Its a real pain but I was able to do it as I had to when I removed my tiptronic transmission. It was much easier to get to the upper bell housing bolts by removing the rear plenum.

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I had little problem getting at the rear AOS bolt, but can't get at the left side bolt. Seems there is a wiring harness (I think) and other hoses that are blocking proper alignment of my socket to reach it.

Just to give you a visual. This is from an '02 996 C2 but it should be similar for your car. As you can see, the inverse "u" channel on the AOS is partially blocking access to that manifold bolt with a socket. On top of that, there's a very fat harness right on top of that bolt also, depending on how that harness was tied down. That's why step #2 is important in this situation. Another way is try to use a 10mm stubby wrench to get on that bolt. It won't be possible in this photo as that fat harness is in the way but it may not be in your engine.