My 1998 STS suffers from a rough idle. The following message also appears in the digital display each time I turn on the car:
Service Idle Control
On occasion, I also get the following message:
Service Suspension System
I have pulled the error codes and get the following:
AMP U1064 – Loss of Communications with DIM (History)
IPM B1340 – Air Mix Door One Movement Fault (History)
IRC U1016 – Loss of Class 2 Communication with VCM or Loss of Communications with PCM (History)
PCM P0550 – Power Steering Pressure (PSP) Switch Circuit (Current)
RSS C1761 – Right Front Position Sensor Input Fault (History)
So it looks like P0550 is the only current code. Could a bad power steering pressure switch cause the idle control problem or the rough idle? Any other thoughts?
You might have a wiring problem with the PS pressure switch, that is part of the "idle control system" so when that code sets it is causing that message to display.
The PCM watches for high PS pressure indicating a turning maneuver. At low speeds the computer compensates for the load on the power steering system by increasing the idle.
The rest of those codes are worthless unless you have problems with those specific systems.
The "rough idle" concern could be related to incorrect idle speed control or you could have a bigger problem. Hard to tell from what is posted there.
Actually, I have experienced occasional difficulty turning the steering wheel when at low speeds recently. When it happens, it feels like I don't have any power steering at all. But it goes away within a second or two.
I'll have to see if I can test the PS pressure switch this weekend. I think I saw a posting on how to do that.
Check your IAC valve, make sure it is functioning, also I would inspect the MAF and TPS sensors, and lastly check for any vacuum leaks. Are you pulling the codes using the onboard dash screen? I did so also and found that I was missing a few codes, went to a friend's shop and connected a computer to it and retrieved more codes, had service idle message - turned out to be a bad TPS sensor.