97 Bonneville SE, 250K original miles, this car has been a real champion of longevity with little more than routine care and maintenance. Its been a Florida car its whole life. Right now I'm

The car has been idling high at startup for over a year, as high as 2800 rpm. The rpm will increase with electrical load, (turning on the A/C, headlights, etc) and (usually) drop when removing the electrical loads. The car will idle high when coming to a stop light and will usually drop to normal when coming to a complete stop though sometimes I'll have to turn off the A/C to get it to drop. Looking at the Idle Air Controller with Torque Pro, it can read as high as 122 counts out of 255, which let's me drive in 4th gear at 50mph without touching the gas pedal sometimes. Normal idle, around 800 rpm with the A/C on, is around 50-70 counts. The IAC is doing what the PCM is telling it to do. But why?

The car is at the shop and the (competent) mechanic, and myself, are stumped.

IAC, PCM, ICM, EGR valve, LIM and UIM, Valve cover gaskets, and Throttle Body have been replaced with new or from known good, running engines. No vacuum leaks have been found. The PCM is NOT throwing a DTC P0507 Idle Control System HIGH RPM code.

Please help.

hi, I would first try unplugging the MAF sensor and see if the issue changes. I would also inspect the throttle plate and linkage to be sure it closes properly. give that a try.
cheap and easy!!

_________________
poverty forces one to do unorthodox things

2000 SSEi
past rides:
1996 SSEi
1992 GTP
1987 Grand Am

MAF has been unplugged and the throttle plate and linkage have been changed/checked with no change in the high idle situation.

ok, I would next move to throttle position sensor. see what it reads at Key On Engine Off, and idle. with the tb being replaced, you might need a reset/ relearn to 0%. I would put koeo, and unplug the tps. turn key off. plug in tps and start car. - is tp at 0% at idle

_________________
poverty forces one to do unorthodox things

2000 SSEi
past rides:
1996 SSEi
1992 GTP
1987 Grand Am

I know I'm late to this ball game... But I would check and see if there are any Transmission Range Switch failure codes