Hello
Just finished rebuilding the heads and putting the engine back together. It seems to work mostly ok, except for a high idle condition: feels like the throttle plates are binding somehow:
- I disconnected the accelerator cable, just to rule out any cable influence.
- You start the engine and it idles pretty well (750-800rpm after warming up). The minute you accelerate (opening the throttle by hand) and let go, rpm's stay high, like 1500 rpm and it never comes back to idling. Notice the throttle mechanism in this condition should be fully closed, at least is touching the stop screw. I can then manually push the throttle closed a bit further (it barely moves), and the idle comes back to normal.
- No computer error codes whatsoever.
- I took the throttle body apart. Plate shaft is mounted on ball bearings and they run smoothly. Only noticed some resistance where the throttle spring collar rubs the body. I cleaned and lubricated the entire mechanism: same problem persists.
- My TPS does not allow for any adjustment i.e. it doesn't have mounting slots. So it just mounts on a fixed position. I haven't measured sensor voltage, only because the computer doesn't throw any codes.
At this point, I think my issue has to do with throttle body only, but I could be wrong. Should I look into something else? Again, if you push the throttle body a bit further, idle goes down to normal. I've also checked for vacuum leaks, just in case.

 

If the PO dismantled the throttle body it is possible the throttle blades don't quite line up with the bores now but that should be easy to fix, just loosen the screws that attach them to the shaft just enough that they can be shifted and realigned.

 

I had the same problem with mine. The throttle plates would get stuck in the bore and I was able to physically push the throttle closed and it would idle back down. I fixed it by turning in the throttle stop screw some so that it could not close enough to get to the spot where the throttle plates would stick. Do this with the engine off and once you start the truck it will automatically learn the new throttle position for idle. Did this to my truck about a year ago and its been idling perfect since.

 

The throttle stop screw should not be adjusted unless someone else has already done it. If someone has tampered with it maybe the factory paint is still on the screw and you can get it back to close with that. I believe the plates will only stick if the screw it screwed about all the way in?? If the throttle body screw is still properly adjusted with the factory paint and no one has tampered with it, your problem is not the screw adjustment.
People try to adjust idle with that screw and there should be a sticker on it saying don't adjust it. It is not there to adjust the idle. Sandy