I have been chasing down a poor idle condition for about 6 months now. I FINALLY found it!!! Whoo-hoo. I started doing the worst thing you can do, replacing so many things at once to try and fix the problem, I created many new problems. It all started with a bad TPS. I replaced mine, but messed with the stop screws on the throttle body essentially closing the butterfly valve. So, needless to say, my truck still ran like crap. I couldn't figure out how to get everything back to normal settings.
So...
I bought a used TB off ebay (40$, like new) and just stuck it on yesterday. I started the truck up, and to my amazement, IT RAN GREAT!!! Wow, all the power back (all it ever had anyway) NO chugging or coughing or sputtering while slowing down.
However, when I came to my first complete stop, the idle went WAY high, no tach to tell exactly how high. It was quite high though.
I started off after the stop, and the truck continued to run great while driving, and at the next stop the idle went high again. It was like the truck didn't want to go out of high idle. So, I stopped again, and turned the idle screw down some, which did lower the idle, but it also made it chug a little when starting from a dead stop (nowhere near as bad as with the TB butterfly closed, but noticable.)

Now after all this long-winded background story, here is my question:
What can make your idle go high (kind of "stuck" in high idle/cold start mode) ? I ask this because all the power is back from the TB swap, but I'm thinking there is something else wrong with it to keep the idle high, rather than just turning the idle screw almost all the way down to keep the idle down. I think that is just masking the real problem. Some of my poor running to begin with seems to be due to my turning the idle screw almost all the way down on the old TB.

Thnaks for any and all information/help!
Jason

Make sure you don't have any vacuum leaks. Check the throttle cable and dashpot as well to see if they're binding up.

All new vac. lines put on last week, all nice and tight. How do I check the dashpot to see if it's binding?
Thank you for your reply!
Jason

There's also an idle adjustment screw on the throttle linkage assembly.It has an allen head screw with a locknut.It can be kinda hard to get to.It's on the passenger side and kinda underneath the throttle body.Reset the main idle screw on top of the throttle body and adjust the one underneath.Good luck! <img src="/forums/images/graemlins/cheers.gif" alt="" />

That adjustment screw for the TB is the one that I messed with last time and it took me about 6 months and 300$ in parts to figure out that's what was causing my horrible idle and general crappy running condition. (By the way, NONE of the parts helped it run better then, but I'm sure they can't hurt performance now that the new TB is on there) That's the one that adjusts the amount the TB butterfly is open, correct?
Jason

Does a quick tap of the throttle drop the RPMs to normal? Might have your throttle cable adjusted to tightly. Should be just a little slack between the the casing and the throttle body connection. Also, look into replacing the return spring on the throttle body. A fatigued spring is almost as good as not having one at all.
~Darin <img src="/forums/images/graemlins/baby.gif" alt="" />

Darin,
A quick tap of the throttle doesn't seem to get the idle back down. I am lost

double check the tension on your throttle cable then. Not sure if you have one of them old style 10 lever throttle linkages or the good kind thats just a wheel on the butterfly shaft, but either way, make sure there is sufficient slack in the cable so that it can return the butterfly to IDL location. Another thing, lube the throttle cables casing.

Just to make sure Im understanding this all correctly, with new throttle body installed the engine behaves perfectly normal and fine, until after driving and coming to your first stoplight, then it goes into a high idle?

Make sure your cooling system is fully purged of all air, that all hoses and vents to the plenum are sealing tightly and arent cracked. Next- make sure your idle is to spec and not set to high. The fact it runs normal until coming to a stop after driving it, makes me think the problem is really simple and just being overlooked. Hows the condition of that return spring? Next time it does this, pull over soon as you can, get out and manually work the throttle shut...if it shuts to the IDL location with your hand, the problem can be easily solved.

~Darin <img src="/forums/images/graemlins/baby.gif" alt="" />

Bust out the carb cleaner and spry it where the throttle body meets the intake, does your rpms go up? I had a similar problem untill I found a large vacuum leak, I used an early style t/b gasket for a late model throttle body. Hope that helps.

I have a very similar problem. I have a manual tranny w/tach. When the engine is cold thre rpms is around 1500 or so. Let it warm up w/o moving it and the rpms drop to 1000. After I drive it and come to a stop, rpms are at 1500 sometimes 2000. I can manually push back the throttle cable/dash pot and it will idle around 900. Sometimes and only once in a while the rpms will idles around 900 when I come to a stop. Mine seemed to happen after I cleaned out the butterfly valve (w/o taking off the throttle body). I don't have the money now to throw at parts that may or may not be the fix so I just live w/ a high idle. I think it could be an easy fix, I'm just scared <img src="/forums/images/graemlins/shocked.gif" alt="" /> to mess w/ the engine. Suspension and stuff like that, I don't mind getting into, but w/ engine stuff, I just seem to make matters worse. Hope you find out what is the cause. It may make my life easier <img src="/forums/images/graemlins/smile.gif" alt="" />. Sorry I couldn't be of any help.

Sid