I have a 90 civic Si that began stalling at redlights (only after it is warmed up) a few weeks ago and the check engine light came on. The ecu code told me that it was a water temperature sensor problem. Sure enough, the sensor was reading 8000 ohms when it should have been 400-600. I changed it out and the check engine light cleared, however the car still stalls. I checked for vacuum leaks etc. and found no problem. I cleaned the idle air control valve, still stalls. I changed the idle air control valve with a new honda valve, still stalls. No computer codes showing. I have tightened up the throttle cable to keep it from stalling. The idle occilates between 800 rpm and 1200 rpm at irregular intervals and not rapidly. With the throttle cable tightened, when it is running at 1200 is when the should idle properly, and likewise when it is running at 800 rpm is when it would normally stall.

My only guess is that the ecu is either telling the idle air control valve to open or close but not regulating as it should.

Is there something else I should do before investing $$$ in a new ecu?? Am I missing something??

Thanks, Steve