Hope someone can steer me in the right direction here. My 89 4WD pickup has some funky erratic idle issues. Here are the scenarios: when starting in the recent cold weather the idle is way up above 2000RPM and then starts going to about 2200RPM then back and forth between the two speeds. Once the truck has warmed up the idle doesn't vacillate like that but stays around (too high in my opinion) 1100RPM. At times after it is warmed up the idle will drop really low, like 500RPM or so and want to stall. Might there be a common culprit behind all these issues? The truck has 206K miles on it and I haven't done anything to the engine in the year and a half that I've owned and driven it. Anyone have any ideas where to start? Thanks, Shmukster

 

It isn't uncommon to have debris build up on the throttle plate which makes it stick open a little. Some carburetor cleaner and a toothbrush will fix this problem.

Also, check and adjust the TPS since it plays a huge roll in idle quality. The specs go out of tolerance over a period of time.


http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml