Driving it off the cliff - 986 Forum - The Community for Porsche Boxster & Cayman Owners

I am about ready to find a cliff and let this car roll off it. Getting tired of fighting it. This is on my 2000 tiptonic Symptoms - Misfire codes P0300, P0301, P0302, P0303 Replaced so far: Plugs coils spark plug tubes oil cap vacuum canister vacuum check valve vacuum lines all O2 sensors aos short aos line long aos line (royal pain to replace) maf varicam solenoid cam plugs intake plenum rubber connectors Had 1 shop do a smoke test which they said didn't leak, but dont trust this shop cause I knew the canister was cracked when they did the test. Removing the oil cap does cause the engine idle to change. HOWEVER, when putting the cap back on, it causes the engine to die as it adjusts idle back. This is the very strange thing. Video here, but the audio isn't all that great. https://youtu.be/drOXhEi4npA

Here is what fuel trims look like.

One potential vacuum leak source that is often overlooked is the brake booster line. It's seldom a problem on these, but worth looking at. I chased intermittent troubles on a Cayenne for a few months before I figured that one out.

Yup, thought of that one last night. That one appears to be good. Removing it you can hear & feel the vacuum on that line. I have had this in the back of my mind cause my brakes are rock hard, especially compared to my 03. Both have brand new pads & rotors so they should "feel" similar.

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Vacuum leaks can cause misfires but your codes are for just bank 1. So I would look for something that would affect vacuum on just one bank.. General or common vacuum leaks are going to affect both banks. First thing I would do is a vacuum test with a standard vacuum test gauge at idle. I would look to see if it pulls vacuum within spec. But more importantly I would want to know if there is any action from the needle. You want a steady needle like it is painted on the gauge face. If the needle ticks that "could" indicate an issue with valve timing. Which could cause misfires. That is where I would start as a first step it is a simple and cheap diagnostic test. It could "possibly" tell you if the issues is related to valve timing or not.. If it tests out good with a rock solid needle then valve timing is good. Then I would look for other sources of vacuum leaks on that one bank. So something within the intake system on that head. Also the electrical wiring to the coils and the injectors. I think the last two are unlikely mostly because misfires are affecting all three cyl. Possible but unlikely. Also did you record the freeze frame data when the codes where set? It would be interesting to know the conditions when the codes set and if they set under the same or similar conditions every time.

Durametric doesnt do freeze frame unfortunately. Torque does but I haven't see it very useful but will get that info. Does anyone know what the actual vacuum numbers should be or what the specs are? I have seen different numbers and can't seem to find them in the fsm. Can only see 25 psi at the brake booster in the fsm.

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A general spec. is 18-22 in.hg at sea level. Deduct 1 in.hg for every 1000' above sea level. So if your in Denver at 5000' and your gauge reads 15 in.hg that would be 20 in.hg at sea level so you would be good. But remember the most important part of the test is noting the needle action if any. What I am really looking for is: is your valve timing ok.

2 shops checked timing, including the dealer and both say it is in time. Checking myself also confirmed it. That is about the only thing I think that is good. Keep the ideas coming. Oh and thank you too

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I would still do a standard vacuum test. There may be some value in doing so.

I did one a while ago (about 2 months ago. if I remember right it was around 14 but will do it again tomorrow to see what it's at.

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just for kicks what elevation are you at??? 14 in.hg sounds a little low!!

St. Louis isn't that high from sea level around 450-500' That 14 is a big improvement after I did a new canister, vac lines, check valve & plenum rubber. If I have a leak the only other place I think it could be would be pass side (bank 1) intake gaskets.

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I don't know if it's physically possible, or for that matter advisable on the Boxster. But back in the day we would spray some starter fluid around the intake manifold gasket area on the old British sports cars. If the idle speed increased that was a sign of a vaccum leak at the gasket. But cars were much simpler then, maybe this isn't a good idea on a modern car if you can even get to spray in that area.

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That reading indicates a vacuum leak. Also indicates late ignition timing dependent on action of the needle. What does it idle like???? Normal smooth??? or lumpy?? or hunting?? When it misfires do you ever feel it??? Do you have an idea of what RPM range it happens??? Also big question I failed to ask sooner any mods?

Easy one...No mods I'm one that keeps things pretty stock with engines. Never feel the misfires. I can see them in durametric but that's it. I would call idle lumpy. It isn't hunting like what happens on lawn mower engines. Here is the weird thing. When the car is cold at startup the SAI turns on as it should. During this time that the SAI is on there are NO misfires. Which indicates an air leak to me but I would expect to see misfires on more then just bank 1. I need to pick up a better vac gauge. The only thing I have right now is the gauge on a mity vac which I dont think is all that good or accurate.

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So RPM kinda rises and falls at idle. If you sit in neutral and hold the RPM at 1500-2000 does it smooth out??? SAI injects air into the exhaust. Misfires occur in the cylinders. So no relationship between the two. Maybe no misfires on cold startup because it is on a richer open loop fuel map. So possibly the richer fuel mixture is compensating for the unmetered air of a vacuum leak at first startup. You can get a vacuum gauge at places like O'riellys for around $25.00 Try to get one with as big a face as possible. Also some still show the green zone, late ign. time area, late valve timing area. But they are getting hard to find. Not many people use them anymore. Everyone has got to the newfangled smoke machine. They only tell you one thing. Vacuum gauge if you know how to read the needle can tell you a hell of alot.

Do I get that right that you`re only getting the misfire codes when the engine is hot? Perhaps the CPS is failing?

I get misfires as soon as the sai turns off. So I would say...warmish & hot. Tomorrow I will get it out and get Durametric to do some logging. What would be good for everyone to look at? Thinking... rpm, misfire on each cylinder, what else ? Have a vac gauge coming tomorrow. O'rileys was out as was HF.

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If vacuum test shows low vacuum with a steady needle then that says vacuum leak. If lumpy hunting idle changes to smooth running at 1500-2500-2800 RPM then those two things together are a very very strong indication of a vacuum leak. since your misfires start as soon as your SAI turns off the vacuum leak is most likely some where in the SAI system. Would be interesting to compare rough running of cyls. on bank 1 to cyls. on bank 2 I think Durametric shows rough running for each cyl.