My 96 T 100 4 cylinder 5 speed has developed a strange high idle problem, it idles high when the engine is warm. Not sure what rpm, the truck doesnt have a tach, but abnormally high for sure. Tapping the accelerator slows it down for a few seconds, but it creeps right back up.
I noticed some slack in the accelerator cable, tightened it up, and then the accelerator would not move at all!
I guess a small amount of slack is normal then?
The adjustment screw never touches the cam, so thats not the problem.
Any ideas/suggestions???

Yes...the accelerator cable is supposed to have some slack/play in it. It shouldn't be tight at all. ;)

How many miles do you have? I'm gonna guess yer IAC (idle air control) valve is gunked up with carbon. It should be located under the throttle body and is electrically controlled by the ECU. If the valve shutter is gunked up, it won't close all the way and allows more air during idle. ;)

Cleaning is cheaper than replacement...but it's yer money. Best method is to pull it and physically clean it. Manually cycle the shutter to make sure it's got the full free range of motion. :D

Well, she's only got 578,000 currently, but just around 60,000 on the new motor, but I plan to put on lots more before we part company!
Despite the high miles, the truck runs/drives quite nicely.
I tried the end play trick I read about here, no dice, so will go after the IAC next.
Thanks again for the help, this forum is awesome! I'm spending way too much time just browsing through the forum looking for things I can fix on my truck.

I swapped fuel filters on mine to get the idle to drop. It was full of crap.

It was IAC shutter, gunked up solid.
Running like a top again!

It was IAC shutter, gunked up solid.
Running like a top again!

Thanks fer the follow up...glad it fixed yer issue. Got any piccies of yer bad IAC valve and care to post them? ;)

BTW...did you clean it or replace it with a new one? :D

Sorry, didn't get any photos, but it turned out to be simpler than I thought. I took it the throttle body loose and was able to tip it up enough to clean out the shutter with some spray Seafoam cleaner/lube stuff.
Worked it back and forth with my finger until it moved freely, closed everything back up, hooked up the vacuum hoses and wires and fired it up. No more high idle problem!
Now I want to do the Seafoam cleanup, but will have to wait until I'm out in the boondocks somewhere, dont think my neighbors would appreciate the smokeout.
Thanks for all the valuable information, that would have cost a lot of dough if it had to go to a shop.