I have a really serious problem with my 1997 Ford Ka. I start the engine - no problem; it starts promptly and idles itself immediately. And it runs that way fine until I touch the accelerator. When I do that, it revs up, but when it should come back to idle mode, it doesn't. It just stops. I poked around and I found the spark plugs black - a clear indication of too rich air/fuel mixture.

I replaced the IAC (idle air control valve), MAF (mass airflow sensor), O2 sensor and the throttle position sensor. There was no change. And my old sensors work just fine on a car of the same make, model and year. If you have any ideas about what could be wrong, please tell me. I have no more of my own.