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YOUR RESEARCHRough Idle - Help My Local Dealer
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Check pending codes
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Performed · outcome unconfirmed · Original poster
Under warranty a long time ago, they changed a bunch of stuff on another 40th AE with similar issues.
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Performed · outcome unconfirmed · Original poster
I don't think it's the flywheel either, more because last november when i bought the car they changed the RMS under warranty, and i said change the clutch as well, and make sure you check the flywheel.
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Suggestion
Once the O2 sensors are hot enough to work the DME can use their readings to know something's amiss and adjust fueling at the problem bank to try to bring the 02 sensor readings of that bank into spec.
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Suggestion · Original poster
I don't think it's the flywheel either, more because last november when i bought the car they changed the RMS under warranty, and i said change the clutch as well, and make sure you check the flywheel.
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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.
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.
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.
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!
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.
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.
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
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.
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.
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.
I have a similar problem: 1999 C2 with rough idle at all temps (cold, warm, and hot). No CEL. I've replaced the coil packs and spark plugs. Throttle body is perfectly clean. Rough idle is unchanged with and without MAF connected. Disconnected battery to reset ECU, no change. Again, no CEL.
Local indy checked everything, could not find any problems. They are competent, having found vacuum leaks on my previous Boxster. They gave up.
Have appt on Friday at local dealer. Will report what they find.
The misfires and lower compression on bank 2 are clues.
I would suspect a VarioCam Plus solenoid/actuator is acting up or the Plus (variable valve lift) is faulty. My money is on the Plus.
The DME will attempt to adjust fueling to bring the O2 readings into line and this can go far enough the engine can misfire. The engine can misfire too if the valve lift is not what the DME commanded. Fueling, ignition timing, and valve timing are all selected with the proper valve lift being in effect.
The lower compression numbers on bank 2 cylinders suggests the cylinders are not filling as completely as those on bank 1.
There is a road test that can be done -- it takes a Porsche diagnostics computer and two techs to do the test -- that verifies the VarioCam Plus variable valve timing and lift are working properly.
However, I trust temp sensors were checked for reasonable readings? An air intake sensor or a coolant sensor that reads goofy for awhile at cold start or after can cause problems.
I have to point out that tearing into the VarioCam Plus system is an expensive undertaking so one wants to be sure to eliminate other possible causes of the symptoms before well, undertaking any work on the VarioCam Plus hardware.
Thanks Macster, my dealer is still consulting other dealers for ideas on this, i will definitely run your suggestions by them.
How does VarioCam Plus act during start up and open loop operation? My idle is the worst at the beginning. It just doesn't stay high when i first crank the engine. It drops the same instant i start the car to the point it almost kills the engine, the whole car shakes for a bit, and then it shoots up. Don't understand what could tell the engine to drop the RPM's right away while the engine is still cold! A faulty Temperature sensor maybe, but i would've thought they would check that before they did compression test!
This is great info from in any case, i really appreciate it. Thanks!
Briefly at cold start the VarioCam Plus selects low valve lift.This reduces pumping losses and reduces fuel consumption and emissions at this time.
In open loop mode my understanding is low lift is selected under some low rpm low speed low load operation conditions. The same reason: to reduce pumping losses and improve fuel economy.
There are various things that can cause the rpms to rise then fall as they do in the case of your car's engine.
Too many to cover here. Besides I'm sure the techs' list is even longer, more complete than mine. Many (probably all but one) do not apply in the case of your car.
But a lot can be eliminated because what your engine has is a failure of some kind limited to one bank. This rules out a lot of common failures and this includes any related to the intake air temperature (with one exception I mentioned in an earlier post and which I won't cover again here) or a coolant temperature sensor which I suggested in an earlier post forgetting that only one bank had the signs of trouble.
The failure limited to one bank should -- but I'm not a trained/experienced Porsche tech -- should have the focus on what bank systems are separate.
Fuel lines are one. But this does not look to be a fuel line problem.
What it looks like is a VarioCam Plus problem.
Since the engine is cold the 02 sensors are not working. Thus the DME uses fuel/timing maps. These are based on the engine being at a certain level of operational goodness.
So the engine starts. The DME works the sensor numbers (MAF, intake air temperature, coolant temperature to name a few) and comes up with fuel injector pulse widths.
The pulse widths apparently agree with the needs of cylinder of one (the "good") bank but not the other bank.
Now how can the two banks differ in the amount of air they receive and thus react differently to the same amount of fuel?
Well one answer is the intake valves of the problem bank not being in the state the DME has commanded.
Now cam timing differences can be detected. The DME selects an advanced timing setting and then uses the camshaft position sensor along with crankshaft position sensor to know the cam timing is where it should be.
But there is no real way to know the valve lift is as it should be. There are no sensors which measure this directly.
There are ways to confirm to a certain confidence level the lift is as it should be.
Once the O2 sensors are hot enough to work the DME can use their readings to know something's amiss and adjust fueling at the problem bank to try to bring the 02 sensor readings of that bank into spec. But it probably won't succeed. The effects of the low lift failure is so severe a condition the DME can't adapt to it.
There is the possibility if the engine was run long enough -- I am *not* advising you do this -- there would error codes related to the rich or lean threshold of one bank being reached.
However, I was told when my Boxster's VarioCam solenoid/actuator failed the cylinders can misfire before the DME reaches some rich or lean threshold.
Please do not use the above as a club to beat your techs over their heads to get them to look at the VarioCam system.
But do discuss with them and get their input. If not VarioCam what then could account for this behavior, the misfires?
What can be done with reasonable effort and cost to eliminate other possible and reasonable explanations for this behavior and other signs of trouble?
Figured i would just fill you in on the latest on this issue. I have been persistent with the dealer on resolving this issue, and they took my car in again. They can't seem to get any codes out of the car other than old misfire, so they disregarded the complete variocam solenoid theory. They think it is flywheel that is causing my rough idle when started cold. I was skeptical at first, and still am a bit, but did some reading and apparently a bad DMF can cause misfires and rough idle. DMF should be in on Wednesday.
Nothing, they replaced nothing. They acknowledged that there is an issue, but whatever testing they did with their diagnostic tools did not produce any definitive results that would point to an issue with a specific part. How they pin pointed the flywheel this time around, i don't know. I do have that loud clank if i shut the car off without holding the clutch in, which as far as i know can point to a DMF, but other than that, i have no idea.
Even the flywheel will be replaced under either the third party warranty that i have or they will pay for all the repairs/parts. I bought the car from them and i explained to them that obviously the car came with this ongoing issue, and they agreed. All these tests and diagnostics has not cost me anything.
Glad you're covered, I thought your dealer may have been parts replacers and you were footing the bill. Hope a resolve is near. Is this your first Porsche ownership?
Yup, first. Was looking for a 997 but dealer had this 40th come in on a trade in. Local car. Fell in love from the second my fat *** touched the natural leather
No i didn't import it, apparently it's impossible, because they don't meet some silly law in regards to bumpers in North america. I spend 3-4 months overseas every year in Europe, so I just drive it then. It's parked at my friends garage. Work of art in any way. So much attention to detail. Interior is just sick! Mine is just a 1.9L JTDM Diesel but pulls like mad. Love it, but unfortunately can't bring it here although i would love to. With Fiat buying Chrysler, Alfa will be back in North America soon. I think 4C will be the first one. Unfortunately 159's they quit making in 2011.
Well, you have to go with what the techs (the real experts) have to say. If they say DMF then so be it. I obviously could be wrong, and in fact hope I'm wrong, in that a DMF is a lot easier to put right than a bank of VarioCam Plus hardware.
Best of luck.
The DMF is easy to test but trans has to be out. Sounds a little odd. Don't know how the DMF would know if the engine is cold or hot. If they are going in anyway, I would consider clutch, IMSB, etc, while your there.
I don't think it's the flywheel either, more because last november when i bought the car they changed the RMS under warranty, and i said change the clutch as well, and make sure you check the flywheel. This was 3000 miles ago, the tech said it was fine. Now it's so bad its making my RPMs bounce? Either way if i get a new flywheel, great, it won't fix the problem i am almost certain, but i am done with them.
Nice man! I want to import a 2011 159T spec from Romania. But ya, it seems impossible but I think I have a way around all the fuss... I'll let you know if it works!
