Not familiar with your car, but a suggestion. At idle when it is having this issue, can you under the hood accelerate the rpm manually with the cable? Trying to isolate the issue, mechanical, or still a fuel issue. I know you post not dtc.

 

If the issue remains, I'd recommend a compression test.

 

I appreciate all suggestions. Yes, I can manually rev up the engine under the hood by operating the throttle body, it operates pretty normally while not under load. And it seems to idle okay most of the time, it only hesitates/runs abruptly when pulling away from a stop or accelerating while moving slowly. The irritating thing is how it is intermittent; it might go for a whole trip and operate smoothly, and the next start up a few minutes later, it will be bucking like crazy. That's why I examined, and cleaned all the electrical connections even though they looked clean and were tight.

I can't imagine that it's a compression problem, that wouldn't account for the times that it runs normally. And I did double check for vacuum leaks under the hood. I only wish the darned CEL would go on and show a code with an OBDII reader.

 

Sounds like something in the gas tank with what you post. You changed the fuel pump, so I would think if there was something floating around in the tank you would have found it.

 

Still playing around with it. Thought it might be a worn wire shorting on the 7X crank sensor but that was a short lived cure; again it ran just great for one trip, then next start it ran so poorly that it actually stalled while idling. CEL light came on a few days ago...no codes with three different readers. Light went out. Another symptom - while it bucks and jerks when loading it up in drive (not moving with brakes on) it pulls strong without hesitation when doing the same thing in reverse. So I'm still thinking there's a wire shorting out somewhere with engine movement, just haven't found it yet.

 

Steam or Diesesal? Bent side rods can cause jerky performance. If they have been handled wrong they can get bent

 

I put the van on hold until the weather warmed up. Thanks to these posts https://chevroletforum.com/forum/ven...00-rpm-101149/ and https://chevroletforum.com/forum/ven...problem-29946/ I was convinced that the 24X front crank sensor was the problem. And it was, it seems. Pulling the harmonic balance was easy, and since the engine mount under there was a mass of rotted rubber I changed that out at the same time. It's running well now and took about three hours, half of which was cleaning road grime.

Thanks to all who chimed in with suggestions!

 

Just an update, over a month later and the van is still running well after that 24X crank sensor change.

 

o Reilly's told me it was some gas vent on top of tank(100$ part) I got tank dropped,but I'm lost

 

I can't see how that would cause the engine to run rough; it may cause a P0440 code due to a problem with the Evaporative Emission Control System, do you have such a code? What are the symptoms of your problem?

The part you're looking for may be shown in post #5 of this thread: https://chevroletforum.com/forum/ven...plugged-97505/