Any ideas welcomed, really...at a dead end. But the ongoing saga of the slight and irritating misfire/ stutter of this car continues. I cannot in good conscience do any further maintenance until solve the misfire. And I'm serious, I'll scrap it- I'm just about done chasing this ghost.
It's a 99' 2.8L/ Avant/ Tip (obviously) Owned for 2 months. 112k miles.
So far I have replaced, swapped, verified good: Plug wires, Coil pack, Plugs, CTS, Throttle body, MAF, Fuel rail + injectors+ fuel pressure regulator, vacuum lines.
Symptoms: The things starts and Idles just great. Actually doesn't drive half bad. But down the road, at almost any speed + part/ slight throttle and just slight/ medium load the thing will start to stutter, I assume it's misfiring but it seems VERY contingent on throttle position and load (rpm).
While it's "stuttering" if you give it some gas the whole car shudders a little and it accelerates pretty well, then just great above 3500 rpm. But normal driving this thing is a ****. It's completely ******* annoying and this car isn't worth this kind of headache. I've taken it to 4 shops and given them my list of things I've done and they get a blank look. I can tell It will be expensive.
It's throws NO codes, no CEL, readiness passes every check. I've run some logs and watched MBV w/ VCDS and one thing that doesn't help at all is "misfire recognition" for all cylinders goes from 'enabled' to 'disabled' as soon as you touch the throttle. Then back to 'enabled' after enrichment (1/2 throttle?). So misfire recognition in the ECU is useless.
My ONLY lead right now: It's a drive-by-cable car so when I unplug the Mass-air-sensor the thing goes into limp mode (5th gear) and it difficult to drive, but otherwise the symptom/ misfire is gone completely. My brain says that means something in the fueling system is the problem. But what?
NONE of the things I've done have made any change at all.
Can it be the ECU/ injector ground circuit? EGR valve?
it's the blue one...help save it!

 

you dont buy a car for those reasons.buy the one you want.....or wait awhile and buy something you like without all the expectation and heavy load.

 

I'm not even sure I understand you? What the? I'm not buying the car, I already own it...I've owned the car for a couple months, and while it was a decent deal I've been chasing this problem since the 1st day. I also own the other car i the pic.
I'm not sure what you read.

 

Have you replaced the ignition control modules? I believe on that car there are either one or two three channel units on the front of the engine under the plastic cover. On the older 2.8 they were brown and there was one and it fired each cylinder at the top of every stroke (wasted spark). These are pretty reliable but they can go bad, usually when they do they completely kill the spark in one channel (possibly two cylinders), that makes for rough running which sometimes feels smoother at higher rpm's. It should trigger a misfire code although it did not in the older OBDI engines.

You may want to post a full scan of your car on the Audiworld VAG-COM site along with the symptom relating to the "misifire recognition" issue. Someone from Ross-Tech will respond and they can be very helpful.

 

Have you run SeaFoam through everything? Have you had the motor mounts checked out? Do you only get the shudder when you give it gas? What happens when you let off? Does the shudder immediately go away? If you shift manually, does it change any at all? Is it only in fifth gear or, if you hold it in third, does it also do it? Does it do it only at certain speeds or any speed where the engine is below 3500 rpm?

It COULD be a driveline problem, such as a torque converter clutch going bad but it could also be a lot of things mechanical with the car. For example, if the cam tensioners are acting up (not getting enough oil pressure until you get above a certain RPM) you might get something like you describe. A faulty O2 sensor can give a false reading and give you the same type of problem.

Keep after it.

Bob

 

Sea Foam? Yes and two full bottle of Lucas Injector cleaner. No change.
Also changed ALL injectors and FPR.
Motor Mounts check fine, and I personally don't see a problem withe the driveline. No clunk, rattle, whine. The very slight 'shudder' happens only when you give it some gas to accelerate out of the hesitation. The hesitation/ stutter happens in all drives modes, A/T, TIP and in a gear (down from 'D').

I've considered a trans problem..it's not impossible..but..just doesn't feel like it.
As far as Ignition control modules- you mean COIL right? this car has the single 3-pair coil pack right above the PS pump. Yes. Replaced it. Does it have an ICM too? I can post an autoscan...but there are no errors...it'll just say what ECU I have really. I do need to ask why the misfire recognition quit when throttle is in enrichment stage, because THATS where it hesitates.
I may just have to get rid of this thing- I t would be easy to blow $2k on it and never figure this out.

 

Had you done the below?
Tranny fluid & filter change
All differntial fluid change

 

Have not done those things yet. I'll tell you, the 3 places I've taken this car for a diagnosis don't see it as trans problem.

I have found today though, that after driving the car, when parked and not running- if I disconnect any of the small vacuum lines on top I don't find any stored vacuum. No *hiss* that I think you usually get.
Where's the vacuum canister...in a fender well,...hidden under a headlight?

 

In my 1995 the canister is under front wheel well's liner, passenger side.
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By the way, don't you have a throttle position sensor in your '99?
You mentioned pretty much everything else being replaced, including the throttle body, except the position sensor.
If you have no recognition/read from the sensor, then would you think that the ECU can figure out for itself the butterfly flaps' position?
Just throwing it out there...

 

Your car should not go into the limp mode with your MAF sensor unplugged... In anycase, I would suspect a bunk MAF. I know you said it is good, but I heard some cases where brand new MAF sensor was bad. Where did you get it? Can you return it for a new one?