Contacting Members

Unfortunately the name of the member is not highlighted -- too bad. His question describes the condition of my car exactly, though I'm not too worried about the tapping of ISC motor. He writes:

"1990 Cadillac El Dorado Idle Speed Control
Engine Performance problem
1990 Cadillac El Dorado V8 Two Wheel Drive Automatic 135000 miles

When ignition turned on, idle speed control motor pulses about 3 times. I can feel it at the gas pedal. Engine starts rough from cold with low idle speed and no power to drive off. Soon warms up, power is good, but engine still misfires on light throttle. When ignition turned off, engine warm, idle speed control motor pulses about 17 times.

Throttle position switch gives correct voltages, have changed idle speed motor and spark plugs. No vacuum leaks found. Any other ideas?"

I would add a rough idle as part of the symptoms. When stopped, in gear, the intensity increases and often the "Service Engine Soon" light comes on.

I've been chasing this since I started driving it (inherited from my father). In the last 8000 miles I have replaced: distributor cap, rotor, plugs, wires, PCV, fuel filter, TPS, ISC, ECM, and applied a BG fuel induction cleaning kit to clean throttle body, fuel injectors, fuel rail, and fuel tank. I'm beginning to suspect the injectors, and plan on checking for shorts next. Any other suggestions?

BTW, when the "Service Engine Light" comes on, it triggers an E30 code - ISC RPM Out of Range (the only code).

Also, Linder Technical Services describes these 1990 4.5 vin "3" Cadillac Mul-Tec injectors as one of their "dirty dozen" problematic injectors. Not sure the best approach to use if it turns out one or more are shorted -- very expensive.

Finally, (after checking for GM Bulletins) I need to investigate the ground at the block, and make sure that is not part of the problem. GM wrote several Bulletins, and eventually added a bracket at the starter to fix the problem.

Thanks guys. I have the Service Manual (thanks to Faxon Auto Literature), and have worked through the flow charts (E055 is not set). The TPS has been set at 5 volts. You're right about the diagnostics. Even though the system is OBD I, it is fairly sophisticated with a lot of information available from the PCM/BCM through the on-board Electronic Climate Control (ECC) panel and the Fuel Data Center (FDC) panel. I just haven't been able to put all the pieces together yet.