Ive had a horrible engine vibration from low idle all the way to around 1500 rpm. After many hours of research and trial it seems that just slightly turning in the full power screw has eliminated the issue.

I cracked each injector line, bumped the timing advanced 1/8 inch, replaced trans mounts, double checked the lift pump and ran truck on an IV bottle. I also swapped a poss bad injector, removed the exhaust system, played with various idle speeds and checked the motor mounts. All of the above did not remove the bad vibe that was created by the engine. It would fizz a soda it was so bad and in drive or reverse I could not hear the engine over the rattle of everything on the chassis and body.

I think there is either an injection pump or injector set issue to pursue further but the truck is running much smoother without replacing the transmission or any expensive parts. So far.

Just an update hopefully will help out someone in the future and be easy to find.

 

You can get the same problem if the cam isn't indexed properly on the throttle shaft

meaning if you take the lever off of the shaft, and didn't notate the position of the indexing lines and put it back wrong you'll find out really quick that it just won't run right....

 

Thank You for this update.
I have the same problem after doing a little home tuning a few months ago. At first the truck ran fine, but then I started having the same problem you describe. Idled fine in park or neutral, but once in gear the rpm would drop, and heavy vibes especially after it warmed up. I thought maybe the idle screw had backed off, but if that was the case then it would have a low idle in park as well. I'll have to give my power screw a small turn and see if it smooths me out too.

 

Yes thank you for the update...too often people look for solutions to their problem in a thread...then never mention if/how/why it got solved.