So, here's a hard problem for you guys. I searched, but couldn't find anything that matched excatly, so heregoes.My '97A4 recently began to have issues starting after being driven for some time (after coolant reaches operating temp). The engine cranks, catches, but then fails to reach a stable idle and shuts off. After a signficant period of time, at least an hour or so, the car will restart fine. While running, idle is erratic (varies by about 50-75 rpm) and low(~800 rpm after cold-start). Now, for the complications. Whatever the problem is throws the code for the idle stablization valve. However, after replacing that, the problem has failed to disappear. O2 sensors have also been replaced to no effect.

Interestingly when the car fails to start, if one removes the cap from the coolant tank under the hood and then tries to start the car with the cap off, the car runs fine, albeit with the aforementioned slightly lower idle speed.

That the coolant thing helps and that other posts of similar problems mention the coolant temp sensor leads me to think that that could be the problem, even though something else is throwing the code. Thoughts? And thanks in advance

-Drew K.

 

i had the exact same problem (minus the idle stabiliziation code) but the problem was the coolant temperature sensor. Since your car is a 97 I would replace it anyway, as its relatively inexpensive and narrows down the problem (or fixes it). Pick one up from ecstuning.com. I got a bottle of G-12 and the sensor with retaining clip and o-ring for around $40 shipped. that would be the VERY first thing i would replace with the problem you described