Well, at least it does not seem that I am alone in this dilemma. My 1990 V8 Quattro has been a trouble free little beast for many years, but alas it is time to start digging into it. This problem started a few months ago and has progressively gotten worse. The car will start up fine and will run all day. The problem seems to be that it will not restart once it warms up for anywhere from an hour to twenty-four hours. Now I did have a small pin hole in the gas tank which was recently repaired. I was told that the back pressure in the fuel injection system was the culprit but this does not seem to be so. Now my next list goes something like...fuel filter, fuel pump, temp sensor (OT sensor?), fuel pressure regulator, leaky injectors, plug wires, throttle position sensor, O2 sensor, or based on one scarry post here possibly the RPM sensor or flywheel teeth? Well, if anyone has any helpful tidbits, I would greatly appreciate it. Until then I will be testing away. Or possibly just getting the old beast out to a location that has the VAG 1551/1552 test computer.
I had same problem with my V8 (4.2L 1992 model), and in my case the trouble was located at ignition timing sensor and RPM sensor. Both are same parts. The trouble shooting to locate these parts were not easy, but after replaceing these parts, my V8 has been running without any trouble.
