|
Check idle air control (IAC) and coolant temperature sensor (CTS). If the temp sensor is reading too cold excess fuel will be sprayed, therefore high idle. O2 sensor reads rich mixture and then tells computer to not spray so much fuel, leading to low idle. Which will result in surging. Which is exactly what you are describing.
Have someone put a diagnostic Scanner (not a code reader) on it and read the output of the sensors. The check enging light may not come on unless these sensors are reading out of range.(negative voltage or excessive voltage). If your engine is obviously warmed up and the scanner says your engine temp is 32 degrees, that would be your problem. Or if it shows excessively less than normal temperature.
Also check the air intake temperature (AIT). this can cause similar problems if not working properly. And of course the obvious vacuum leaks.
The most important part is to find someone with a proffesional enhanced scanner.
|