99 xj with high idle, slow return to idle and false codes
I have been working on a friends XJ recently and it has me at my wits end. to start, she had to jump it about two weeks ago and crossed the cables to her battery, she did not crank it that way, but removed them cables when she realized the mistake. a couple days later she called saying it would start then die immediately. I initially advised a new alternator, however, after reviewing this forum, I decided to check the IAC and battery. the battery checked out and the IAC failed, so I replaced it with a Borg-Warner part. That fixed the initial problem of dying immediately, however, it began to idle high, around 2000 RPM. Also it would not return to a lower level of idle if you gave it any throttle. (if you brought the RPM up to 3000, when you let off the throttle it would stay at 3000, unless you put it in gear at which point it would drop to 1100, and start the process over) This was obviously a bad TPS, so I changed it, again, with a Borg-Warner. I also took this opportunity to give the throttle body and IAC housing a good cleaning. i put it all back together and fired it up, no change. I flashed the PCM and it ran normally for about 5 minutes. it then bumped back up to high idle. Flashed the PCM again and it began running normally, I let it run like this for a while, checking different parts and listening with my stethoscope until i though it was going to be ok, packed up my tools and put got in the drivers seat for a test drive. idle jumps back up, this time w/CEL indicating bad TPS, i have bought bad sensors before so I got ahold of a new one and installed it, flashed the PCM, now its throwing a bad IAC code as well as a Bad Speed Sensor code(?) clear it, start it, same IAC code. Check TPS and IAC voltage, both are good, removed battery and cleaned and Di-electric greased all connections, it's still acting up. I finally decided to join up on here to bring you my specific issue to see if you guys have any thoughts?