high idle

my 1990 bronco xlt 5.0 e40d will not idle down. i pulled codes that pointed to the iac and the tps. i replaced both. nothing changed. ive replaced plugs , wires , cap and rotor. ive done a vacuum test on the manifold, did not indicate a leak. i vacuum tested every one of those little hard plastic lines under the hood. i can not find a vacuum leak anywhere. i replaced the gasket between the throttle body and the intake manifold.

in park it idles at either 1500 or 2100 rpm. it doesnt fluctuate its just one or the other (?)

in drive it idles at around 900 rpm

in reverse it idles around 750-800 rpm.

what is going on ?

is this possibly a trans problem ?

is there some way the intake manifold could have an air leak that wouldnt show on the vacuum test ?

anybody ?

I have had 3 Broncos that I work on, mine included that had this problem. The plate that the throttle linkage clips onto, on the throttle body. For some reason gets bend downwards, Unhook the throttle cable, the tv cable and the cruise if equipt. Look under the plate as you open it wide open, then let go, see if the throttle closes all the way. Close it by hand to see if it was shut all the way. If not bend the plate upwards slightly, and try again. See if that helps. If thats not the problem theres an E clip holding the plate on the shaft, remove that, remove the plate. Clean the shaft, I took an emery cloth to the shaft. Clean the grease out of the plate where the shaft goes through. Grease it slightly and reassemble. Make sure the plate doesnt bind like I stated earlier. Also you will notice a rivot type thing hanging out the bottom, that sometimes hits the throttle body and limits your wide open throttle

or it could be that the idle ***** needs to be turned in or out or just take it into a shop and have them tune it

1982 bronco lifter said:

or it could be that the idle ***** needs to be turned in or out or just take it into a shop and have them tune it

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ive been reluctant to mess with that ***** as my chiltons guide and a little sticker under the hood both say not to mess with it. is that how the factory obtains the correct voltage for the tps ? i noticed in order to adjust mine without messing with that ***** i had to enlarge the mounting holes on my tps. am i adjusting the tps incorrectly ?

no offense from this newb but i refuse to take it to a shop thats where it was when i bought it.(my buddy had been throwing money at it to have his mechanic throw parts at it ) its not my daily driver and i have a mustang project looming over me ( that i wanna do a carb to efi conversion to ) so i figured learning the ford tricks on one that already runs would be the place to start.

thanks for the input.

that was the first thing i looked at just to make sure the linkage wasnt binding in fact i fabbed up a bracket for the throttle cable just to make sure it cant move around at speed. seems odd that something so important for good signal ( tps) was only secured at the firewall and throttle body. the whole cable would flex with pedal travel when i first got it so i made the bracket just to eliminate that possibility. i didnt however go into the detail that you did on the throttle body itself. can you guess what the first thing i do today will be ?

thanks for the input

well guys just came home with the bronco. first time shes been here in two months. turns out the plenum gasket was shot. replaced that and shes purring like a kitten. now onto the rear window motor.

thanks to you guys who responded.

hey bob whats up with the rear window? What are the symptoms? If you need help lemmme know i just finished fixing mine.

noahsdad said:

hey bob whats up with the rear window? What are the symptoms? If you need help lemmme know i just finished fixing mine.

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IMO my problem on my 91 was a intake manifold vacume leak. The bolts loosened my and caused the leak. after some lock tite and a 45star racket problem solved.

yo!