RedEye

So, I've been having issues starting in the morning. Car will crank forever (1000 amp battery) but not fire. I searched and found the most common cause of this is the crank position sensor, which I replaced. Hated to throw parts at a problem I hadn't diagnosed properly, but my code reader doesn't work on this car. I have since ordered a VCDS cable but it won't be here for a while.

Anyway, after I replaced the crank sensor it seemed to be fixed for a while. I've since figured out that it wasn't, it just seemed like it because the weather warmed up considerably. As soon as it cooled off again, the problem returned. Now that I've realized it's temperature related, I've noticed it will start after much cranking as long as it's above 13-14 C, then stumble a bit until the temperature gauge starts moving. After that it runs normally. We've had a few hot days this week, around 29 C, and it starts and runs just fine. This morning at 11C it wouldn't start, period. This afternoon at 28 C, started normally.

So my theory is that a sensor is reporting a much higher temperature than it should. My question is, does anyone know the failure modes of the coolant temp sensor and the intake air sensor? I know the CTS on my E30 reads negative a zillion when it's shorted -- if anyone can confirm that either of the A4's sensors read too high when they go bad, the parts are cheap enough to go ahead and order without waiting another week or two for my cable to come in.

seanf

they fail in all kinds of different ways, wifes 2.8 the guage would go up and down but would report normal temps to the ecm so the car ran fine, the cheap aftermarket one I installed in my car wouldnt make it up to 90, it always reported 75C on the cluster and to the ecm. Buy a new green sensor from the dealer and replace the one at the back of the head. Its cheap piece of mind.