As long as this idle surge/hop doesn't do it while cruising down the road when you hit a bump. That could be a broken plunger return spring(s).

 

No it does not do it hitting bumps. Only at idle.

 

Mine does the exact same thing!! I thought I was the only one with that problem? I just attributed mine to wear in the IP, I checked everything else. truck runs great, also does it worse when cold. Cold as in engine cold and ambient temperature cold. When it's warm it seems to be less noticeable or nonexistant. If you aren't careful it'll die on me when I put it in neutral at stoplights, and when making turns.

I'm not even sure when it started. It wasn't even relatively close to any mods though. It even stayed the same when I installed my 366 spring and new piston lp??? I thought it may have been where I lost a thrust bearing, but after new rods and mains it's still there.

Steven