I have a 1990 f150 302 5.0 automatic 4x4
Im getting codes 12,13,33 and 31 on koer. I changed the tps and it still idles really high at 1700-2200rpms even after warm up. I unhooked the negative battery overnight with no change. While running i unplugged the iac valve also with no change. I reached inside the TB and blocked the two iac ports with my fingers with little change and can feel the suction on my finger from them. Checked for leaks with carb cleaner and no idle drops at all.
I have read many posts on here and am new to the EFI stuff. Most experience in carb engines. Should i replace the iac anyways?
Im stumped here guys and money is tight and this is my daily driver. Any help would be appreciated.
Also this started after i cleaned the TB and iac valve so i checked the vacuum hoses in the area and most other places to no results. Im hoping is not a upper intake gasket but it ran fine before the cleaning. Thanks in advance guys!

 

With the engine idling and the intake hoses pulled off, put a piece of cardboard large enough to cover both holes over the TB. It will suck the cardboard up tight against the TB. If the engine keeps running with this in place, then you have a large vacuum leak that is letting in a bunch of extra air, enough to keep the engine running. You want the only air the motor gets going thru the TB. If the engine dies, then I suspect your throttle plates are not closed enough. Have you adjusted the base idle screw on the TB at all?

 

No i never touched the idle screw...if i close of the tb completely it will bog down and die but the slightest air i give it with keep the idle at normal operation. I even plugged the two holes to the iac with my fingers and no difference. So its getting air from somewhere i believe but tried the carb cleaner method with no idle drop and definately soaked the intake base. I turned the tps clockwise when i installed it so that let the truck start up every time now. I can see light on the edges of the tb butterflys in the tb when i hold it up to the light. New tb maybe? No air passage holes on the butterflys themselves so i figured thats why they needed the small gap around them.

 

time to check all your vac lines. with that high of idle, its either multiple broken lines or a big line, like brake booster, is at fault. spray carb cleaner, while running, around the lines and brake booster to isolate the problem(s). when the idle gets even higher, you know you've found a leak.

 

Ive tried the spray method and got no change. Just got a multi meter today so im going to check my circuits today

 

Don't forget to check inside the cab for brake booster vac leak. You don't need to spray it, that one you can hear with a closed cab.

Iac might be stuck, take that apart and check it/clean it. They get pretty gummed up.

Make sure the throttle cable is not sticking. Easiest way is to just look at the throttle body armature and confirm its at rest with the high idle.

Then check sensors, starting with tps.

 

Ok thank you...i checked for leaks in the cab. None found. I cleaned the iac the same time the i cleaned the tb and got a bunch of build up out. Everything moves free in the iac. Also cleaned the back of the tb when i had it off to change the TPS as the new one the previous owner put on looked new but had a code for it so i changed it. I even plugged off the IAC holes inside the throat while the engine was running. The idle dropped very slightly and i can feel the suction from the IAC on my finger tips when i blocked them. But the idle still reved high. Im getting codes 12,13,33 on koer test and code 11 all clear on koeo test with 31 in continuous. Ill be testing my egr but i dont think that it will cause a high idle will it?

 

If your egr tube is broken, it'll be a vacuum leak every time the egr opens. If the tube is broken, you'll hear the "tick tick tick" of the exhaust leak under load. I don't think that's your problem.

You definitely have a vac leak somewhere if you can block or unplug the iac and it stays running. Take each tube off the tree on the intake manifold one at a time, block the port on the tree of the removed line, when idle goes to normal you know which vac circuit to pursue. You may have a leaky intake manifold also, but carb spray would have likely indicated that.

 

Ok thank man. Really appreciate that. Ill do that when i get back home and post my findings. Again thank you so much!

 

Ok i unhooked all the vacuum ports and plugged them one by one...if anything when i unplugged them they introduced more air and made the idle go down and loping til i plugged the port and everything ran smooth again just revved at 1700rpm. I didnt drill the holes out on the tps because the old one didnt either so maybe i will go back out and check my volts to see if it is out of range.

 

Ok im getting .09 on closed throttle and 4.4 on wot. So those read good. I did notice if i forced the Tb closed really hard while its running the idle goes down to normal. As previously mentioned, i saw light coming through around the throttle plates when i had it off to clean, so....maybe new TB??? too much gap between the butterflys and the Tb housing? This all started after cleaning it so im thinking i cleared all the crud that was keeping in in check. Any ideas? Truck does have 158,xxx miles so maybe the Tb is just gone.

 

is your throttle body "stop" resting on the idle screw before you forced it closed? that'd be sticky throttle cable / blade.


you can adjust the idle screw and see if that solved it.

 

Yes it is hitting the stop first...as i force it, the plate that hits the screw bends slightly to allow the blades to close more. I just heard ford dont want you messing with that screw as it is factory set. Should i adjust it? It has no way to unless i clamp on a small pair of vice grips and turn it. It was idling great before the cleaning. Will that drop my tps below 0.9v at closed throttle?

 

yes, ford has indicated that "it shouldn't be touched", and yes you should adjust it. I long ago removed the little stud and replaced it with an actual bolt that I can adjust easily on the fly.


if you jack anything up so bad that it doesn't work right, which you wont, you can just grab an entire throttle body from the jy.



adjust the screw.

 

Will do!!! Ill post back. Thanks man, it truely is awesome i found you and this forum.

Fix my problem with a 0.05 cent screw!!! I think after a while of those tb blades working back and forth for 25years, they tend to wear down and the only thing keeping out the extra air getting past them is the gunk we clean out of the way. Or the butterfly shaft gets a little wore and needs more slack after cleaning the tb to close that gap. HUGE props to you sir for the info and i thank you for helping me get my girl back on the road. God bless and CHEERS to you sir!!!