vanner

This is the first time I ever posted on a form. I have a 1995 GMC G2500 conversion van ,2wd , 5.7L , 50,000k miles, excellent cond. , It suddenly started doing the following in the morning when cold. It starts good but when I begin to drive slowly while holding the throttle steady, the RPM start to drop off to aprox 300 RPM over about 3 to 4 sec's, then sudden jump back up the proper rpm. and begin to drop off again. It will repeatedly do this while I drive for aprox. 5 min. until it warms up then operates normal. If it sat aprox 4 hrs it will do the same thing for about 2 mins because it did not sit all night and warms up faster.Even when stopped and idling when cold it will do the same thing. It never stalls and if you feather the throttle twice then push the pedal hard it will accelerate normal right up to hyway speed and drive normal. The engine lit never comes on and there are no codes stored. I would not describe this as Surging because the RPM's drop down then come back to normal. has anyone experienced this before

Rednucleus

My 93 Suburban did this as well and turned out to be a distributor problem. If I remember something was loose - advance mechanism?? - new dizzy fixed it

mikeatpriestlake

could be an idle air control valve problem. also, try unplugging the TPS while it is doing weird things. if it starts running ok then the throttle body went to zero angle, and it could likely be a tps. Try cleaning throttle body and IAC also. hope this helps.