Nedster

So i have this issue of rough idle, especially when cold. The car would surge up and down when started, it would go as high as 13-1400 RPM and then the very next instant, it would drop down to 5-600 RPM and the car would start shaking and engine would start boggin down, so then it would jump up again to like 1200 RPM, and then drop down again, and then eventually it would stabilize, but still run rough, even the exhaust would sound OK, but then all of a sudden it would seem to lcut off, and then go back to sounding continuous. All this is followed by intermittent vibration through the seat. (I changed engine mounts so it's not that). Once it warms up and the RPMs drop, it runs better, but still rough and bouncy (the needle) and with the intermittent vibration in the seat.

The dealer thought it should be looked at, so i did an overnight drop off so they start it up all hooked up in the morning. They spent all day on it and found nothing wrong. Even did a compression test, and went in with a cam and engine interior looks new.

Apparently a while back, they had the same car with same issue but under warranty, so they started replacing parts one by one, but nothing fixed it. They ordered a new DME for it, but the guy crashed it in the mean time. They want to try putting this DME in my car. That's about the only thing they got for it so far.

Just wondering if you guys have any suggestions as to what might be the issue here? Thanks.

Imo000

If the new DME or any other new part doesn't fix it, tell them to take it off and put the old part back on.

pszikla

did they check vacuum on the engine?
the hunting rpm at idle can be a symptom of a bad AOS.
Pete

Macster

What Pete said. AOS.

A goofy test: Try to remove the oil filler tube cap while the engine is idling. If its hard to near impossible, even impossible, AOS. If it is not hard then it could still be the AOS. You just caught the AOS when it wasn't sucking, too bad.

Another possible explanation is the VarioCam solenoid/actuator is bad, at least on one bank. I hope pending error codes were read? When my 02 Boxster's VarioCam solenoid/actuator went out the idle was like that but no CEL. However, there was a pending error code. I do not recall off hand what it was but it will either be there or it won't.

Nedster

The service manager told me they did a full engine compression today and that everything was spot on. Also, from what i understand, they visually inspected (with a camera i assume) all the valves, cylinder walls and everything else you can see, and that it all looked like new.

I left the car over night, so they could hook it up to the computer and check all the sensor operation and actual values at startup and idle. I assume they checked all pending codes then.

It's gonna stay another night for them to try the new DME and a new cold start in the morning. Service manager mentioned that the shop foreman is considering it could be some barometer inside of DME that can't be tested??? Thats how i understood it anyway. This is well beyond me so i don't really know what to even add to that.

As far as the oil cap, i did take it off couple days ago without too much effort. The car started running funny and seemed like it was gonna just die, so i put the cap back on.

In any case, thanks for your inputs guys, i will run it by the service guy tomorrow when he calls me. Cheers!

KrazyK

Im assuming this is a Porsche dealer because you said warranty work on another Porsche. I could be wrong.

Sounds like a huge air leak of some kind, AOS or something else. Especially if it gets better after warmed up. Any symptoms before this started?

I would think it should be throwing codes like crazy. Surely they checked this first. Your mechanics sound clueless to me if they are just guessing and randomly changing parts.

Nedster

No, it's the one and only Porsche dealer in town. Also where I bought the car. They haven't changed anything on my car. Under warranty a long time ago, they changed a bunch of stuff on another 40th AE with similar issues. But I agree with you, don't understand how you just start swapping parts just because they are free.

Not much for symptoms, car was parked over the winter, wasn't driven for months, i thought it was bad gas, but the issue was not going away.

I've checked it with a durametric tool a few times before, it never showed any codes, and i assume that they checked that first before cranking the engine this morning. Even if they didn't should be easy to recreate them.

Vacuum leak is always gonna be my suspicion, but i doubt they will find it if it is. They dismissed it if i remember correctly saying the problem would not be limited to only at idle if that was the case. Who knows, my hopes are not high about this getting resolved over there, but we'll see what they say tomorrow.

alpine003

Do they have a smoke machine? Sometimes it's easier to track a leak down with it.

Cosmo Kramer

Coolant temp sensor to the DME? If the DME thinks the engine is warm instead of cold it will run lean causing the symptoms you describe.

TomF

Try swapping out the regeneration valve. It takes five minutes and a failing one can cause the symptoms you describe. At about $100, they are a wear item anyway, so its worth a shot.

996 110 129 53 Regeneration Valve from Throttle Body for Fuel Vapor System

Best,
TomF

Macster

Parked for months during the winter?... Mice. Though I would think the techs being at the car would have spotted any signs.

Still, ask the techs to look for mice sign. They can do damage that can have the engine acting very weird.

KrazyK

I think hes lost faith in this dealer. Cant say as I blame him.

Macster

Agree. Sad. With an engine manifesting such behavior one would think the diagnosis would be relatively easy. Guess not. But I'm willing -- for a tiny bit more time -- to give the techs the benefit of the doubt.

Just about when you think you've seen everything, something comes along to make you humble again.

Nedster

Well, three days at the dealers, but no solution, or fix. Just some vague ideas of what it might be. Apparently they are talking to some people from Porsche NA about possible solution. Rather then me typing away i just took a snap shot of their report. They haven't charged me for anything and are still looking into it, so i am not too ticked, but would be nice if they just come up with a fix.

Nedster

Looks like this isn't going anywhere, dealer is asking me for ideas, geez