I have a 1997 Cadillac Concours with 126000 miles on it (automatic) that I bought off of Marketplace. When I got it, it ran fine for about three days. I turned it over to go to work and the RPM's wouldn't drop below 1250 after five minutes of warming up. I turned it off and back on and the high idle went away for a couple days (having only driven a few miles a day during that time). I take her for a longer spin and the RPMs go up in Park, Neutral, Reverse and Drive. Which made for REALLY rough shifting. I replaced the IAC and reset the ECU on my own by disconnecting the battery. Same problem. I take apart and clean the throttle body and reset again, same problem. The MAF is intact and there are not vacuum leaks (I made one by over torqueing the bolts on the MAF tube but have a new part coming in). I don't want to go to the Stealership just to have them tell me I need a new PCM which if that's the problem can replace on my own for way cheaper. Has anyone dealt with this in older Cadillacs or in general?
Have you scanned it for codes and data?
There are no lights to indicate a code. At this moment in time it would probably pop a vacuum leak code because I broke the MAF tube. Gonna swap that in and scan it. When I got a new catalytic converters put in last week my mechanic said they saw a 420 something code but couldn’t get it to duplicate.
Not all codes cause the check engine light to turn on. P0420 indicates a problem with the catalytic converter.
I’ll give it a scan once I replace the MAF tube. I’ll put up another comment if anything shows on my code reader. I got the Cat replaced last week so that code shouldn’t be an issue anymore.