After a couple months of throwing parts at my 92 CSS, I finally fixed the problem. Just for the sake of troubleshooting, here are the symptoms of driving with a bad CTS for a month:
- 1992 Olds Cutlass Supreme S, 3.1L
- New IAC, TPS, ICM, Coils, Plugs, Wires, MAP, known good ECM, Vacuum leak check passed, Injectors tested OK, FPR not leaking, not losing coolant...
SYMPTOMS WHEN CAR IS COLD:
- Car will not start on its own. Needs throttle in order to start.
- Car will die at any speed if throttle is not maintained.
- Idle can be achieved by "feathering" throttle, but only lasts for a few seconds before stalling.
- CES light intermittently turns on and off, but this does not happen very often.
SYMPTOMS WHEN CAR IS WARM:
- High idle (1250-1500 in drive). Car will accelerate from 25-40mph on its own, no throttle needed.
- While rolling, putting car into Neutral causes idle to raise to ~2500 RPM.
- When slowing down, car will maintain a high idle until speed reaches ~3 mph, then idle suddenly drops to ~500 RPM. This happens both in Neutral and in Drive.
- Car lopes at idle and stalls regularly, unless throttle is applied to compensate.
- In traffic, car gets pretty hot. This is caused both by having to keep throttle applied, as well as the fans not working because the ECM doesn't know the actual coolant temp.
I just thought I'd put this all in a thread in case someone ever has the same combination of problems. I hope this can help others in their troubleshooting.