4.3 RPM Jumpping Up & Down.

[boomer49]

Lately I have been running into a weird situation with my Red(this is important,LOL) 1999 GMC Sonoma ExtCab 4X4 auto w/4.3 and 152000 miles in that while driving with steady to light throttle and with or without cruise, the engine RPM will jump up 100 to 250 RPM then drop back down. It does this even when not in full closed loop. It acts like the lockup torque converter is unlocking-locking-unlocking-locking, etc. My scanner doesn't show any codes but doesn't have the capability to do the trannie. One observation is that the percentage for the TPS, which normally displays 4-8% while driving, will jump up to as much as 20% at the same time as when the RPM jumps up and then back to 4-8 when the RPM drops back down. Anyone else experienced this and can offer some suggestions?

[CraiGM]

Yes, Im dealing with it in my Grand Prix. Although I know what it is. Its the transmission lol. I had a couple things go wrong with my trans, and I never got a code or a check engine light for any of it.

Try changing the solenoids in there, or get the trans rebuilt while your at it. Im sure it could use it.

[bluegtp91]

Sure it is the transmission 100%? I know you said it is when the TQ. tries to lock but it might be a CPS...that is a really common issue with the 3800's. Hope you figure it out man!!

[Altoff12]

The Other Day a Impala came to the Shop and the Tech thought the same thing as u did and he had to take it out twice and dig deeper and found that the Pump Shaft Seal was Split and that was the problem......but its just something you can Explore not saying thats the Problem

[4.3chevy]

that started to happen when i bought a truck that had gears that wernt stock you can and make sure that they were not changed by the person u baught it from or u can take ur truck in and have ur throttle possioning adusted