Hard to start A4 with motor warm

Dump ECU error codes and see if there's anything that jumps out, particularly fuel mix errors.

There may be a temp sensor at the root cause of the problem; someone good with a code reader may be able to see if a sensor component has aged beyond its useful life (looking for out of range adaptation values, for instance).

Either way, the best way to attack this kind of problem is through the OBD port...

/daytripper '00 s4 6spd

I would start with the temperature sensor.

Thanks Tony and Daytripper for your ideas.

Tomorrow I will buy the new temp sensor and see if it gives different readings that might stop the warm start problem.

Going from the practical to the theoretical - assuming that my temperature sensor is indeed faulty, how would a new one, reading ca. 5C higher, solve my starting problem?

Thanks, Robert

The ECU uses engine temperature as one of the variables in determining how much fuel the engine uses to run properly for what you are asking it to do.

If it thinks that the engine is warm when it is actually cold it will not supply sufficient fuel to start it. If the ECU thinks the engine is cold when it is actually warm it will send too much fuel and partly flood the engine.

Indeed I have now replaced the temperature sensor, though I only get a couple of degrees warmer. So this indicates to me that I may also have a thermostat sticking open, not making it possible to close the access to the radiator when needed (see earlier thread).

But the car restarts without hesitation, even when motor is warm or hot.

OK - we're now a few degrees colder here, so it's not absolutely certain that my warm/hot start problem is solved, but I have had to warm start it a couple of times today, and it seems to have behaved better than before. In addition, I think I am consuming less petrol than before despite the colder temps, which indicates that the resistance of the old sensor had been unreasonably high (reading colder than it should have), causing the ECU to order a richer mixture. This would explain the difficulties in starting before (15 secs on starter motor) followed by the excessive petrol smell - engine had flooded.

Let's hope that the car continues to warm start well, even once the temperature rises back to what it was last week.

Thanks to all who contributed their advice.

/Robert

Thank you all, this info is very helpful to me. My 99A6 Avant is experiencing exactly same promlem. Please help me with the following:

1. did u change the sensor yourself, if yes, where is the sensor is located?
2. where did you buy the sensor? Many thanks! Bloomsburg