Hi Guys,

I hope I’m not posting this in the wrong place.

I have a problem that forced me to replace my car and so at this point I just want to satisfy my curiosity because it has being bugging me for about a year and a half. The car is a 2000 Audi A4 B5 1.6 ltr petrol (Engine Code: ARM). The problem is that the car sometimes refuses to start when the coolant temperature is in the region 60-80°C. It always starts from cold. In addition to this, the engine revs may suddenly increase for no apparent reason, sometimes hitting 2,500 rpm and remaining there in idle for minutes at a time.

A coolant temperature sensor error was retrieved from the ECU by a local mechanic and he replaced the sensor with a used one he had lying around, in addition to this, he cleaned the throttle body. The issue appeared to be fixed and then gradually after about 2 months the symptoms began to materialise again. I brought it back to the mechanic and the same error appeared on his diagnostic equipment. This time he replaced the coolant temperature sensor with a brand new one. The problem was resolved for about a couple of weeks but gradually began to occur again.

Since then, the MAF sensor has been replaced, the throttle body has been replaced and the air intake system has been checked to rule out vacuum leaks but the issue still remains. I got my hands on an intake manifold temperature sensor in the hope that this could be the root of the problem but after pulling out the manifold it was nowhere to be seen so I’m out of ideas. The mechanic reckons it’s the ECU but I’m not convinced since it’s sealed within a plastic container and there are no signs that moisture got in contact with it.

Any help would be much appreciated.