wrx580

Bump for some help with almost identical symptoms. Here's the deal:

I bought my '99 A6 Avant this past fall. It has run absolutely great until recently. As the weather got warmer, I noticed that the car would stumble about once or twice every day; not a series of misfires, but just a single "miss" if you will, while driving along.

Fast-forward to two weeks ago. The stumble began to happen increasingly often, and it got to the point last week that I was seeing the same sort of behavior that the original poster of this thread saw: horrible misfiring and stumbling while the engine is under any kind of load. If I put the transmission in Park or Neutral, the misfiring goes away. However, it comes back as soon as I put the transmission in Drive or Reverse. The problem seems worse with the AC on as well.

I found this thread last week, and I saw that there seemed to be a few potential solutions. However, I decided to take it to a local "European car specialist" so I wouldn't waste too much time with trial and error (this is my daily driver). Well, those guys diagnosed the problem as a leaky vacuum hose after they tested the intake system. I should have known better, but I had them go ahead and replace it. It had absolutely no effect. After that failed experiment, I decided to tackle this myself.

This past weekend I pulled all the engine covers off to inspect things. I pulled the spark plugs and noticed that there was oil gathered around some of them. I cleaned that out as well as I could, cleaned the spark plug wires and put new plugs in. I also went ahead and disconnected the coolant temperature sensor, as I suspected that was probably the culprit from reading this thread. Well, I went for a drive after all this was done and the problem was gone. I then realized that I was an idiot: I should have gone driving before I unplugged the ECT sensor so I could tell whether it was an issue with plugs that was actually causing the problem, not the ECT.

Well, the next day on the way to work the problem came back, just as bad as before. Now I'm trying to figure out whether I should just order a new ECT, or if there is some other problem that needs to be dealt with as well. Any advice is greatly appreciated.

Thanks in advance! Sorry for the novel.

-Ellys

Quick note about the oil around the spark plugs: I realize that this must be coming from a leaky valve cover gasket. I am planning to do a bunch of maintenance soon, and that is one of the issues I'm going to be addressing, along with replacing the cam seals. However, there didn't seem to be enough oil on any of the plugs to be causing any problems. If anyone thinks otherwise, please let me know. Thanks!

Johann2.7t

whats happening when you disconnect the coolant temp sensor? does the engine default to thinking its cold?

Im having similiar issues with the difference being the car hicups when cruising and at idle. I have no issues when accelerating beyond say 20%.

no codes, nothing to report via vag com.

4Driver4

Walk around to the front of the car and look at the grill. If you see four rings, replace the coolant temp sensor...then reset the code it threw when you drove around with it unplugged.

Do the cam adjuster seals and cam plugs as part of your oil leak repair. Do it soon.

SloopJohnB@mac.com

4 Rings. LOL. Good one!

Edd W

....and clean out the air plenum drains.....

Johann2.7t

any other suggestions to try?

having really weird feelings in my 2.7t, feels great at idle or any amount of throttle.

It feels like the engine skips a beat every once in a while only while keep even steady throttle. Not misfiring, no CEL, new plugs, new fuel/air filters, new coolant temp sensor.

Not sure what else to try or what I can do with vag com. Feels like someone is tapping the brakes slightly which is very annoying!

thanks !

Airbag

So we are assuming you did change the coolant sensor ? if so your car sounds like it is just missing. i think it has to miss so many cycles in a row before throwing a code. Can we also assume you have done the obvious like replace the fuel filter and such ?

You could be looing at coil packs but that is guesing. Without a code you have to determine if it is ignition or fuel. Until that point it could be tough .. even fuel pumps fail and give similar symptoms when they begin to die.

Johann2.7t

yes, new fuel filter,coolant temp,plugs,air filter, etc. According to vag com it doesnt misfire at all. Seems to be much better when cold which is one of the reasons I thought the temp sensor was to blame.

what else can i check via vag com? is there a fuel pump flow measurement?

Airbag

vag com is a communications tool . i don't think these cars have on board fuel pressure or flow monitoring.

Johann2.7t

just did a pressure test and it held 15psi with ease. No hint of leaks anywhere which is bitter sweet. Anywhere else to look?