Hello!

My car is an 88' Sierra 2.0 EFI lambda (101hp).

When car is idling (I mean engine running while in neutral or clutch disengaged) RPMs are jumping pretty roughly from about 400-1000RPMs. When I step a little bit on the gas, then engine is running very smooth. What could be the problem?

Is the idle air valve dirty (and where is it located in this exact engine)? Or air flow meter? But I think air flow meter was okay, because I opened it up and checked resistances for the main air valve and they were okay.

Thanks,
Toms from Riga, Latvia, Eastern Europe