Hey Guys,

First post here and hoping you can help.

1992 F250 351w injected not carb. Idle was hanging and high when changing gears (around 2500rpm)... Replaced TPS, still high idle. Replaced IAC, still high idle. Unplug IAC, idles ok. I replaced with a Borg Warner IAC.
Scanned for codes... nothing related to TPS, IAC or throttle body. Do you think the replacement IAC is just stuck open?

thanks in advance.

Dennis.

 

That's always a possibility. I don't think there is a code for the IAC. At least not on my 87. I had a Bronco II that had idle problems. When I replaced the IAC it didn't help the situation. Hopefully that's the case for you as the IAC is easy to get to. Good luck.

 

What were the codes? Please list by number and when they were displayed.

Please define "ok"

 

sounds like a vacuum leak.

 

i had this problem on my 92 f150 5.0l

would idle some what fine unplugged. plugged it up it would be around 2000,2500rpm.

so i left it plugged in and drove around for a few blocks brought it back to the house and unhooked the battery for about 30mins or so,then it was find. cold start it will idle on high idle for about 20-30 sec then come down, or you can kick it off bye just hitting the gas real quick. its been fine ever snice.

 

No fast codes, Continuous memory codes as follows.
172 ego not switching, lean exhaust - bank 1, ego not switching, rich exhaust - bank 1. 334 EGR (evp) voltage above closed limit.

idles ok means idles at a consistent and smooth 750rpm.

I have also smoke tested the vacuum system - no leaks detected.

 

Easy check on your new IAC valve. Pull the valve and have someone turn the key to "on," NOT "run." The plunger should move in and out with turning the key on/off. If it doesn't move, replace the unit. Same prob. on mine; the plunger was frozen and 2 cans of carb cleaner couldn't free it. A new IAC valve cured mine. Best of luck!

 

Idle RPM @750 w/IAC disconnected is WAY too high, Verify the throttle stop screw has not been jacked. If it looks factory then you have a vacuum leak. The throttlebody can have worn bushings and/or blades and still pass the smoke test.

Your lean code still makes me think you have a vacuum leak. Code 334 means the EGR may not be fully closing. Another source of unmetered air.

 

pastorJim i'll test tomorrow and let you know