I helped my stepson get a 95Z 2 weeks ago. All stock A4 right down to the paper air filter. Opti and intake gasket replaced this summer. Car ran smoother than my 94 until yesterday. Won't idle, it's not throwing any code. Starts right up runs great, sounds great as long as your reving it. Let off the gas and it dies. Put it in gear and it pops and won't go. Any idea's what to check?

 

Check for vacuum leaks and the plug wires for damage or not properly connected. A plugged cat along with a dozen or more things can cause this. If you can check the fuel pressure thats a good place to start.

 

Check the coolant temp sensor in the water pump. Plug probably fell out since you were in that area.

 

Would the coolant temp sensor allow it to rev freely though. It park it revs fine with no strain, just won't idle. Put it in gear and you can't get down the driveway.

 

Sounds like a vaccum leak. Something may not be bolted down or you have a cut in some hoses.
Chris

 

That's what I'm leaning towards, just trying to figure what to check. My stepson called the local shop and they say it must be the opti. i know it can't be as it rev's freely without a miss. I don't want him to take it there and they charge him several hundred bucks for nothing.

 

Do me a favor. Check the hose that goes on the driverside of the intake manifold that leads to the master clynder. I recall one time after putting my intake back on I forgot to hook that hose up and my car would not idle at all. I hooked it back up and it idled fine. Im having a simlar problem not as bad as yours on my 94 LT1, Just did a stroker on it. Back of my egr pipe on the back of the intake has a leak. So check that as well for any air escaping.
Chris

 

It was a vaccum line. Now running great. Thanks to everyone for helping. My stepson is smiling to get his Z back for no cost to repair. And even better he was able to fix it his self.

 

Just wondering. Which vaccum line was it?
Chris