Pulled tbi cleaned carbon build up from pvc port replaced base plate gasket now engine wants to idle extremly high

there is no idle position sensor, there is an iac,idle air control stepper motor that is located on the tbi,throttle body injection unit,there is a tps on the tbi as well,throttle positioning sensor, so if you are looking for an idle adjustment it is not possible to just turn a screw, first you should check for vacuum leaks,a vacuum leak will cause the idle to go up,the block learn will also be up past 128,use a smoke machine and smoke the engine to help detect a vacuum leak first,no leaks found then reset the throttle body set screw to zero,clean the tbi with a good carb cleaner and a little brush,no biding,check tps for correct value, from 0.6 to 0.8 volts at close throttle and up to 4.8 volts at wide open with no voltage drop or glitches,make sure the pcv valve is working properly,if you have idle quality problems make sure all is good,hoses,cap rotor wires plugs,leaking valve seals can contaminate the air intake and play a role in extreme cases. check plugs for a build up of carbon which indicates this. good luck

idle air control valve faulty or have intake leak at the throttle body gasket.throttle cable binding throttle body shaft and plates have lot of carbon build up throttle body need cleaning.

idle air control is looking for base idle. throttle body base idle plate is dirty with carbon. cleaned out throttle plate with carb cleaner and tooth brush. use rags to catch black carbon.open plate.by some one hold throttle plate open with gas pedal. engine not running. after completed, start engine. run 1500 prm for a short time to clean out excess fluid. that should fix your problem..

Hi, the throttle body can get carbon build up, resulting in a low idle, or possible check engine light. The carbon build up can be cleaned. The most effective way, is to actually remove the throttle body, and clean the throttle plate, and air flow ports, with a good spray choke cleaner. This is available at an auto parts store. Once reassembled, the low idle situation will be resolved. Good luck...Coop

My 94 Jimmy had similar problems, until the dirty EGR valve was replaced. We tried a million things, first. But the improvement with the new EGR valve has HUGE.

check for any vaccum lines that may be unplugged.
then remove the air intake tube and clean the black carbon build up from around the throttle plate.use a clean rag only.i think whats happening is at an idle the plate is all closed but for just a little bit for the idle.carbon closes this off and is causing the engine to die at idle.
clean the carbon out very carfully and using some carb cleaner.

hope this helps
keep me posted

jm

These trucks were equipped with a TBI, (Throttle Body Injector). This looks like a modified Carburetor with two large fuel injectors placed over a two barrel throttle plate and venturi body. You need to check the base gasket on this TBI Unit. The base gaskets were notorious for becoming brittle and cracked . If you remove the air cleaner and open the throttle plates you may see a chunk of black hanging out down below the throttle plates. If you see this, this is the base gasket and it cracked and needs to be replaced.
The Idle Air Control Solenoids were also an issue on these truck too. This is a round part that will have a plug on it normally near the base of the TBI Unit. This will just require a quick replacement.

The last thing that it might be is the electronically controlled EGR Valve. This valve used to cause some trouble from time to time, and I know there was a warranty campaign on these parts. the valve will need to be replaced or cleaned if this is the case.

Good luck and hope this helps friend, Keep me posted and here is a link for you to retrieve DTC codes. http://www.troublecodes.net/GM/

On the bottom right side of the throttle body toward the firewall, is the Idle air control valve. Sometimes this gets carbon build up that interferes with the stepper motor. You can unplug it and remove the valve (it unscrews with a 27mm or 25mm wrench; or the medium crescent will work). Once you have it out use a mirror to look into the bore it came out of. If it is plugged or heavy with carbon you can clean it with healthy dose of throttle body cleaner... If it is really bad you can use a bore brush to loosen up the heavy stuff and flush with generous amounts of throttle cleaner.

Check all your vacuum lines since your there. replace the old brittle stuff. Check and make sure the TBI unit is snug and not loose, look for signs of bad gasket material around the base.

Spray the TBI throat and clean the butterfly. You can use a old toothbrush to loosen up the build up and prevent you from using a whole can of cleaner.

Went you have everything reassembled, be aware that it may stumble a little on start up. It has to burn off all that throttle body cleaner.

After is it idling, you can clean the TBI throat by spraying the cleaner down into the throttle while manipulating the throttle to keep the engine running. (do not over rev the engine)

If the condition continues, there is a procedure to check the IAC. It is fairly cheap at most discount part stores. ($35 to $45)

check TPS (throttle position switch)connections and TPS switch are renound for issues may need adjusting base idle, also check pcv hole in throttle body base manifold area clean out throttle body also if carboned up
is also possible this idle air control valve (IAC) is sticky due to carbon build up clean with carby cleaner or some sort of solvent

I just solved this problem on my truck after fighting with it for 2 yrs. Mine is the 5.0 though, check your PVC valve and replace if it is bad. After that Take off your IAC and spray down with carb or brake cleaner and scrape all the carbon build up out of it and work the spring inside. you gotta really clean it out though! After that if it's opening and closing easily put it back together and it should work! you might have to adjust the idle a bit to get it all the way. But after doing this my truck went from a 2000 rpm idle down to about a 700! I hope this helps you!!