I have an 87 Comanche 4.0 with an automatic transmission that idles very high. It has around 230 xxx miles on it. I've been trying to diagnose the high idle problem for a while now and I can't seem to figure it out. When I start it up when its cold in park or neutral, it idles at around 1000 rpms and will fluctuate down to 500 and then back up to 1000 rpms until it warms up. As the engine gets warm the rpms increase and will peak around 1800rpms usually but sometimes will make its way up to 2500rpms. When in drive at a stop it idles at 1000 to 1200rpms when warm. I have replaced the iac, tps, map sensor, I cleaned the throttle body, thoroughly went through every vacuum line I could find and found no leaks. It's not very consistant as some days it idles higher than usual. Sometimes it will idle at about 600rpms after reaching temprature but sounds like its misfiring. When this occurs I turn the engine off and start it back up and the misfire stops but will idle high like it usually does. I've noticed that it never reaches 210 degrees after warm up. It usually runs around 160 degrees. I've owned a few other jeeps with the 4.0 and they all ran at 210 after fully warmed up. I have not replaced the coolant temp sensor yet but I might try that next. Any information on what I should try next is very appreciated. Thank you for reading.
