I drive a 1997 1500 4x45.9 with 136K miles on it. I have been experiencing looping rpm's from the engine while stopped at traffic signals i.e. the motor revs up to 900-1000rpm from 600rpm. I watch the needle bounce up & down until I accelerate down the road. This will happen for two or three days in a row and then nothing--it is fine fora couple of days and then back to the same old-same old. This has been going on for 5-6 weeks.

The problem started when I came back from vacatoin. The truck sat for 9 days in some hot humid rainy weather while I was gone. The initial problem was traced to a dry rotted piece of vacuum hose starting to split that ran from the throttle body to the charcoal cannister.This turned out to be not the problem solver. No error codes come up and the O2 senserwas justre-placed. I have also noticed the engineidle has been high on the start up that past 2 days.

Anyone having some suggestions or prior experience with this type of issue please reply and point me in the right direction. Thanks-in-advance.

 

Try something really simple and cheap likecleaning the entire throttle body with carb cleaner and the gunk off the plunger of the Idle Air Control motor on the back of the TB. If that doesn't fix it, try replacing the Throttle Position Sensor on the driver's side of the TB.