idle is hunting???

1999 C2 Cab. The revs are hunting up and down during idle. At first it only did it with the a/c off and only did it occasionally. If I hit the a/c when it was hunting it would corrected itself. Then it started doing it both with and without a/c occasionally. Now it seems to only do it with the a/c on and not when the a/c is off. When it does it with a/c on it idles at about 1400 rpm and doesn't really hunt up and down jut stays at 1400. When it does it with the a/c off it hunts between 800 and 1200 up and down again and again. Local shop said it was a vacuum leak and the hose in the picture with the red dot just below it is the culprit. Said it goes to back of engine and would take 5.5 hours to replace. I'm skeptical this is it. Since I couldn't leave the car with them he put some JB weld on the spot he said the leak was at hoping it would limit the problem until I brought it back. I also wrapped electrical tape the entire length of this hose and the problem still remained. Anyone know what that hose is and would it cause the problem I am having if it was leaking right about where the red dot is in the picture? Sorry for the ****ty pic but the car is covered and to lazy to take better picture so I used an old picture, plus it's raining here. Just don't want to replace a hose that requires 6 hours of labor and it not be that hose.

pic...

It's the hose that attaches just above the little red dot I put there and then bends up and back and sort of to the left and back into the engine compartment.

That is a corrugated plastic vacuum hose that goes all the way to the brake booster in the frunk. Lots f labor to replace. Usually the leak is from the o-ring inside the "L" elbow right where your red dot is. However, it's possible the hose itself cracked but that is not common as far as I know. It would be good if the shop can smoke test it and send you a vid of where the smoke leaks out.

If it's the thin (like spaghetti) lines, could connect to either the vacuum reservoir or the intake resonance flap actuator. Replacement method is similar. I think you'll need to remove the airbox, the throttle body, and the front plenum to gain sufficient access. Having recently replaced my air oil separator and being familiar with process, I could probably do it in under one hour. Someone less experienced would take longer but 5 1/2 hours seems excessive. If the break in the vacuum line is close to the front of the motor (rear of the car), you might be able to cut the line where the leak is and splice the two pieces back together with a small section of rubber vacuum tubing from the auto parts store, without removing everything.

took the cover off and went for a drive...took a better picture... If you notice I wrapped it with electrical tape from the bottom thimble like thing where it connects and is held on by a C clip, all the way up and past where he said it was leaking and put the JB weld adhesive. Seems if it were leaking the tape would correct it at least temporarily. However not so, even with tape, so I am questioning it. I have owned this car 2 weeks now and this idle issue is the only issue...I'm doing a lot of preventative main., fluids, filters, etc. The biggest PM I am doing is coils, plugs and plug tubes. I am taking it to a very good Porsche performance shop Monday to confirm the other shops diagnosis of this hose. Question: Should I go ahead and do the coils, plugs and tubes and see if this corrects the problem? Or would they have nothing to do with a idle issue? Or should I wait to do this and have the new shop find the idle issue first? I have read many threads that say my problem could be coil or plug related i.e. worn coils or plugs or both. As far as I know the plugs and coils could be original, if not original then replaced in 2004 (11 years ago) @ 22K miles. Car has 60K miles now. Trying to avoid hours of labor looking for problem when it could be coil/plug realated? Which way would you go? Have shop find idle issue before I do coils/plug/tubes, or do coil/plugs/tubes and then see if idle is corrected and if not have shop look in to idle issue?

I agree with your suspicion. I would recommend cleaning the throttle body and the idle stabilizer (using a 9v battery to activate it while cleaning) first and go from there. I doubt the hunting is due to coils/plugs. Usually coils/plugs will give you more problems under load (misfires). Also scan the car with a Porsche tester to retreive any pending codes and also check the fuel trims. Of course last but not least a smoke test is always good.

Can do a throttle body cleaning, but the idle control valve is new to me. Any good video or tutorial you know of?

Not that I know of. Just connect +9v to pn 2 and negative to either pin 1 or pin 3 to make the valve open/close. Then hit it with carb cleaner. You should be able to see the internal part rotate and it needs to move smoothly.

Located the ICV on my engine and know how to remove it and replace the gasket when re-installing it. (Is it necessary to replace gasket?) So I wire positive post on 9V battery to pin 2, and wire negative post to pin 1 or 3. This should make it spin or move or something and as it does this spray cleaner on it. Correct? Going to clean MAF and throttle body first and see how that effects idle. If not resolved, then I'm doing the ICV. MAF was just replaced by PO in September so I doubt it's that. But I'll clean it anyway. Thanks for your help....

You were asking about that specific corrugated line: that is the breather hose from the AOS. See this diagram: http://www.autoatlanta.com/porsche-p...section=104-10 Yes, it can cause a major vacuum leak and that will lead to "hunting" idle. Also check your oil filler pipe for any sign of cracking. Run engine, remove oil filler pipe cap and note change in idle...then replace cap and see if the engine idles any better. Better yet have someone smoke test the whole intake system. And finally, yes, PITA to replace that hose because to do so you basically have to do the AOS replacement job...which in this case I would go ahead and replace it at the same time. My recollection is that folks that pay to have that done get charged 4-6 hours labor. Good idea to clean the TB and ICV as well. I could stand to be corrected but I don't think that hose is the brake vacuum booster line seen here: http://www.autoatlanta.com/porsche-p...section=604-15

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Hi Joe, that is the brake vacuum line. I worked on it before and I also have a car with the engine removed sitting in my garage. I can clearly see that line still attached to the car going to the front of the car. You were thinking of the AOS hard hoses which look similar but they are at different locations. One connected directly to the throttle body and the other to bank 2 engine case.

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All correct and it's good practice to replace the gasket.

Cleaned the MAF and Throttle body and car runs perfect. Didn't do the ICV since the first 2 fixed it. Now..do I believe the mechanic that said that hose is leaking? I'll have another shop verify. But if no idle problems, I'll leave well enough alone. Thanks guys

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Hey thanks Ahsai! That's why I put my disclaimer comment in there. Did the AOS and remembered that hose, but forgot where it went. To the OP, all's well that ends well. You did a good job.

Well, I took it out again just to make sure it was OK. Idle problem returned. So I cleaned the ICV. I hooked it up to a 9V and it just open and closed a bit, Didn't really seem to make much difference cause I could get the cleaner it without the battery. People made it seem like the thing spun around fully and it was essential to hook it up to the battery. Am I missing something here. A lot of sludge and gunk did come out. Reassembled and ran it 20 mileds or so, and seems fixed, just like when I did the MAF, and TB. Maybe I do have a vacuum leak somewhere, possible where the first shop said I did. Taking it to MCK Performance in Davie Monday. See what they say. They've already seen the car and recommended a few things. They suspected a vacuum leak but I didn't have time to leave it with them. The PO only used non-ethanol gas in it because in NC he could get it. Down here I have to use 10% ethanol. I filled up twice. You guys think the switch has something to do with it? Guys at MCK said there was some additive I could use once in a while if I remember correctly. Going to take it for some good runs this weekend and we'll see. Also, as soon as the parts come from Autohaus, I'm doing the coils, plugs and tubes. Maybe by miracle that will help.

Found you a vid. Yours should be similar IACV Testing - Porsche 944 - Idle Air Control Valve - YouTube

Ahsai, Yes it is similar, actually identical in the way it works. However, you said post 1 is positive on mine and 2 or 3 are negative. In the video his positive is in the middle. If, as you say, post 1 is my positive, then it is not the middle one. They are marked, and 1 is an end one. Is this correct? Or did you miss-speak and my positive is in the middle? When I did this on mine with a 9V, the valve indeed turned, however mine did not close fully like the one in the video. There was still about an eighth of an inch gap when it was in the closed position. But, I hooked positive to post 1. Maybe my positive is post 2 which is in the middle. Could this be why it didn't fully close, or is mine not suppose to fully close? Also, I'm not sure the 9V was fully charged, perhaps I should recheck using the car battery tomorrow. And lastly.....I was under the impression using the battery was part of cleaning it, that I was supposed to open and close it as I applied the TB cleaner. Or is opening and closing it just to check operation? Like I said.... since my did not fully close...I cleaned without battery since I could get cleaner in it due to it staying open slightly. Very much appreciate...maybe it not fully closing is my problem....

I never said post 1 is positive. I said post 2 is positive in post #9, which I edited one time only to add the mentioning of carb cleaner. The activation is two fold - to check its operation and to loosen up any cruds after carb cleaner is applied. Btw, I think not fully closed is normal but I'm not 100% sure.

You are absolutely correct, my bad. I miss-read your words... TY

Today I did the spark plugs, coils and the tubes. Everything I removed looked in good order, but good to know it's all new now. Threw in a new air and cabin filter also. Car was still idling bad occasionally and was hoping this would correct it..but it didn't. Let me tell you guys exactly what's still happening: From a cold start it fires up nicely and the first 10 to 15 miles idles great, spot on at 800 rpm with ac on or off. Then out of no where the idle will hunt when stopped now that the car is warm. Specifically, with ac on, it will idle high around 1400 rpm steadily. If I turn the ac off it drops and hunts between 600 and 1000 rpm up and down. I'll drive some more and come to a stop and it might run just fine for 20 or 30 miles when I stop at lights and what not. Or it will do just as I described sometimes. When it idles fine it is spot on and I can turn ac off and on and it stays right at 800 rpm perfectly. If you guys look back, I had a shop say that brake breather hose was leaking. I questioned that because they wouldn't show me the smoke test afterwards. Also I took it home immediately and cleaned the MAF, IACV, and throttle body and the car ran great for several days. I figured they just skipped right to the most expensive thing they could try put by me. Thought the problem was solved but days later it returned. Here is my best guess as it stands.... The weather has been all over the place here in Florida, 60's then 80's, high humidity then low humidity. So I'm leaning towards a MAF problem. Even though it was just replace several months ago by last owner. Seems to me if it were a leak in that hose the idle issue would be constant and not random and certainly not run great for days at a time only to pop up again. Am I wrong? Call me crazy but the idle issue seems to happen when the car is at an incline, i.e. nose up like on a hill. Doesn't seem to do it when flat. Might just be my imagination but I'm spit ballin' everything. Just trying to nail it down before I spend $$$$ having a shop chase it down. I was going to do all the PM I listed anyway so like I said I was hoping it would be corrected with those things. Would a MAF issue throw a code? So far I have had no CEL's at all. Car is fantastic except for occasional idle issue. If you guys can't think of anything else, I am going to hit the MAF with some cleaner again. If that fails, I give up, and she visits the shop. Was hoping I would own the car a couple of months before any costly issues arose. Don't even have a good shop yet to take it to that I trust. Thanks guys...

1) You have the same original problem. 2) You had a shop smoke test the intake and they said it was the brake breather hose. 3) All symptoms point to an intake vacuum leak. 4) You have done everything but address the brake breather hose, or have it re-checked by another shop and get another independent analysis. I know it sounds goofy, but you need to get a vacuum gauge on it while the engine is running. It still sounds like you have a vacuum leak. On a separate note, running down a rough running/bad idle/rough idle/hunting idle problem, I cleaned the MAF sensor multiple times, then finally replaced it with a new one. No CEL ever appeared. Problem solved.

When the engine bay is warmed, the issue starts to show up. This is indicative that one hose is flexing or getting more pliable and causing the leak. Why was the MAF replaced a while back? Was it for idle hunting? The MAF and ICV are the two components which determine idle speed. If the idle speed can't be maintained with the ICV completely closed(vac leak) the MAF will call for a greater supply of fuel to keep the mixture correct. Next time you have it warmed up, and the idle is hunting, take the upstream supply hose off the ICV and block it with your thumb. The engine should stumble and will likely stop running. Let us know what happens after this test.

Ok then. I will pull the IACV upstream hose and report the results as you suggest. And if I can ask, the car sputters and possibly stalls..that's a good thing? If I pull it and block it what else might happen? In other words what am I looking for. FYI. One of the reasons I got this car was to do as much as possible of my own wrenching, I gave up golf and no longer work, so it's fun for me. My thought pattern was, since I was going to do so much preventative maintenance once I got the car, I figured why not wait and see if by chance I hit upon the cause for this idle problem. I am not doing all these things trying to chase it and ignoring the "probable cause", a vacuum leak somewhere. Now that most of the PM items are done and the issue is not resolved I will feel better about taking it to a shop if necessary. That said, I would like to solve this myself, so that is why I'm fishing for suggestions. Oh and by the way...I did have a second smoke test preformed and they did not find the leak where the first shop said it was. The first shop just said "here is your leak" for $900 we'll fix it. I asked to see the test in person or if they video taped it. They just said trust us. Well I walked because I never used this shop before. The second shop I trust but it is a ways from me. I did not let them diagnose further because I wanted to do my PM first and see if it would resolve it. So that is where I'm at. If a few more attempts at the usual suspects doesn't work, to the shop it goes. Thanks.

The ICV is an electrical part, in a hot engine bay which uses a motor to move a shaft. In theory, the control signal to the ICV is an analog voltage proportional to the opening of the valve. The signal is developed by the engine management computer based on the tach signal, the O2 voltage value, and the MAF signal, temp sensor and prolly a few other bits of info. I'm wondering if the ICV is failing under warm conditions where maybe a mechanical or electrical fault is not allowing the ICV to properly control the bypass air to the engine. If you take off the ICV hose, and close it, the engine should pretty much die. If not there's air getting to the engine from somewhere else(vac leak). Alternately, you could ask around on borrowing an ICV and try that with a hot engine.

Turns out it was the ICV. Replaced it and all is well. Thanks to all who helped....

The car should not idle at the same rpm with the "A/C on or off"... Probably means your A/C (compressor) isn't working... Glad you got the "hunting situation fixed though...

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Glad you got it sorted and thanks for closing this thread.

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My guess is prolly the ambient temp was too low to load the a/c compressor or it was not even engaged.

Took the car into have some fluids flushed and the guys tell me the car is still idling rough, very slightly rough, meaning car is vibrating or shaking to much. And that what I consider the idle needle on the gauge as a steady idle, they say it is still hunting oh so slightly. This concerned them, and me also for that matter. I mentioned to them that I had replaced the ignition switch just as PM and happen to also mention that when I switch on the headlights that every so often the lights do not come on immediately or I have to switch them off and back on. This concerned them and they stated that perhaps the ECU was not communicating properly and there could be an issue with the ECU itself. Told me they hard wired the lights to the battery and the lights did not display any failures. So they ruled out a faulty switch and leaned more towards an alternator or ECU concern. They informed me that a code came up that said the alternator was not putting out enough charge. I questioned this because I and another shop had tested the battery and alternator and it came up clean for problems. Wow. Only a month and a half of owning this car and quite frustrated at all these ghosts were chasing. Two Pre PI's and a Post PI when I had it delivered and these issues were not happening. From all this can anyone chime in with some thoughts? Can a weak alternator and/or battery cause these idle issues. Just to be clear the hunting idle to me is virtually non-existent with the new IACV, but to them it is. And the rough idle, meaning the car shaking or vibration when at idle is noticeable to them, yet to me is oh so slight which is why I thought it was fixed.

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I'm skeptical about what your shop said. Your headlight issue sounds like typical headlight switch failing, a very common failure. Can you ask them what error code they saw that said alternator output was low? Btw, is it a shop that specializes in Porsche? Strange they use the term ECU amd not DME. I would suggest you get your own OBDII scanner (the type that can read sensor values in real-time e.g., bluetooth if you use Android phones) or Duramtric, which can show misfires in real-time. Also get this tester for battery and alternator testing. http://www.amazon.com/gp/aw/d/B000EVWDU0/ref=mp_s_a_1_1?qid=1453705389&sr=8-1&pi=SY200_QL40&keywords=innova+battery+monitor&dpPl=1&dpID=4105fQmT1vL& ref=plSrch Idle vibration can also be the engine mounts.

I have the same issue and the OP, but I keep throwing P0302 I have changed everything (coil, sparkplug, injector, wires, leak test etc etc) and still does it.

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Perhaps the MAFs are creeping past their effective dates on the first generation 996s? Clean or replace seems to be the question for some (many) of us.

Asked him ECU terminology and he said yes DME, same thing, it's just what he refers to it as. By the way guys I am using MCK Engineering in Davie, FL. Just to clear things up, these guys are Porsche specialists. They walk the walk, very involved in racing and a great group of very dedicated enthusiasts. Some of what I relay to you guys might get lost in translation. And I've been pretty hard on them with wanting to wrench my own car and just have them diagnose things. And with this mystery idle issue that's been difficult. Just wanted to add this to explain the shop I'm using. Today they have determined that the timing is off. We have narrowed this down to probably water entering the throttle body. When I first got the car I washed it 3 times in a row after doing several stages of paint correction. Not sure how careful I was with controlling the water. I do remember after completion I took it for a drive and is hesitated quite bad shifting from 1 to second and to third. Did this for about the first 5 stop and goes. And prior to that I had owned the car for about 10 days and there were no idle issues ever in the several hundred miles I drove it. So I probably F'ed it up with too much water in the wrong place. Not a fact but a possibility. Going to replace 4 or 5 sensors including the IACV, and the throttle body itself. Going to replace these sensors in a common sense order from, most likely the culprit/least expensive, to see if the problem is fixed. They informed me that only the sensors that are needed will be replaced and only I'll only pay for those. He said the timing could be off due to other things, but that would require cracking open the engine and would be very costly. So we're hoping it's one of the sensors not performing correctly. Basically, what I was told it that the ECU/DME is getting readings from these sensors and because one is not working properly, it is sending conflicting information and the ECU/DME is battling to keep this running smoothly with conflicting information from one or more of these sensors. If it sounds like I'm being flogged for cash here, cause it might given the amount of stuff they done and diagnosis time, that is not the case. MCK Engineering when I first bought the car did a free post purchase inspection and many other things. I was stressing last night about just letting the idle problem go and just drive it. So I was prepared to tell the guys at MCK to just tell me what I owed them. Including several hours of talking about my new car, a brake flush and them having my car for about 5 days, he said if I want to halt things, aside from the $200 brake flush charge he would only charge me 4.5 hours for diagnose time. And he said they had way more hours than that. I've really chewed there ears off and questioned everything, If I were them I would have told me to go to hell and get off the property. MJ, however, as it turns out has been great and talk me off the ledge of of some what I now realize was stupid ways to deal with this situation. MJ from MCK Engineering posts on this board and I just want to make no mistake that these guys are up and up good guys and know their ****, in my opinion. And like I said some of the many in depth details of what they explained to me get lost in translation when I post here. Any way. Hopefully tomorrow or Wednesday all will be good. If idle is solved having him replace transaxle fluid. Said he uses Mobile 1 fluid.

To officially, officially close out this thread... Medevack1, may be helpful to you... Idle air control valve was replaced along with the throttle plate position sensor. Turns out both needed to be change for proper fix. Both these are super super easy to change out as they are right next to each other and nothing in the way as far as getting to them. Two small hex bolts on each to undo and disconnect the both electrical clips. IACV valve has a gasket you should replace, and the TPP has a o ring to replace. Now I now how smooth and sweet this engine should be when dialed in. We are sticking to the excessive water getting into the throttle body when I did the multiple washes that took out these sensors. They were 16 years old to boot. I do remember taking it out for a drive immediately after and the car lost complete power a couple times as I accelerated hard. And like I said the car was delivered to me and ran great for a couple hundred miles. Then after the washes and sputters when I took it out is when it started with the idle issue. Also had them replace transaxle fluid. They used the mobile 1 fluid. Crossing fingers no more unscheduled fixed for the next year, just mods or PM.

Quite interesting. Do you know if there was ever an error code logged for the throttle position sensor?

Yes. But I didn't get the codes. And they are gone for the 24 Hours of Daytona. One code I do remember, they said was something to do with the the alternator not supplying enough juice. Which is when they started questioning it and possibly the battery. Just picked up the car hours ago, had to because these guys are heavily involved in racing and have cars in the 24 hours of Daytona this weekend and were packing up to go there. So my car would have sat in there shop until they got back next week. Thing is with these guys they are **** about everything (which is good). Because of their racing mentality they are used to x-raying blocks and wheels and what-not, and making sure everything is perfect, good won't do, cause on the professional racing circuit good loses races or gets you killed. I think I may pay a little more but really like the way above average attention to detail. Always willing to talk and share great stories. Very relaxed atmosphere. I think most of them have made their money and are sitting pretty and now are very into the racing and the repair business is just a natural extension of the love of Porsche's. They are racing a couple of Cayman's this weekend. If they billed me for all the hours I spent with them talking Porsche's I'd be taking out a 2nd mortgage. I'm 49 and my working days are over. Secretly I like to ask them if I could hang aroung the shop just watching them at their work. They have some great cars there getting serious performance upgrades. MJ was a professional Porsche driver and most the techs are Porsche racing mechanics. ...but I digress...

Ahsai... Is there any posts with your credentials listed. I'm very impressed with your knowledge and interested in your background. If you were in South Florida, a couple of beers and a couple of hours would be very interesting and informative. Rock on....

Thanks Rolex. I'm in South CA but will take you up on your offer if I'm close to you I'm just another home mechanic/enthusiast trying to help my Porsche brethren. I do try to understand all the principles behind and I have a genuine interest and curiousity in anything mechanical, electrical and diagnostic related