1992 IAC Valve Questions

[Airhead315]

Alright, after searching the forums and reading posts regarding eratic idling I decided to check out my IAC valve. I pulled the IAC off and checked it out...not much to see I guess theres no good way of looking at it and making a diagnosis...So I did the next best thing...I put it back in and started the Explorer when it was running I unplugged the IAC valve...no change in the idle at all...there seemed to be no effect. Its Cold out...about 30 degrees so I would have expected some sort of affect on the engine idle a stutter at least. So is this a good sign that the IAC valve has failed and will need replacement? Below ill explain my problem.

Well, its a comibination of two things I believe. First, the car will always idle high, once you shift into gear it has a tendency to want to stall until the engine warms up, then the idle is dangerously high, so high that when in snow conditions the back wheels will make it almost impossible to stop as when I hit the brakes the idle seems to continue to want to push my car. The front brakes will lock but the back tires will begin spinning(at slow speeds) and it will cause my car to want to keep going...I believe this is mostly bad rear brakes...but the extremely high idle cant be helping. Oh, dont think im a lucky one, I have transmission problems too...when first taking off the transmission wont shift into 2nd gear...after a while it gives up around 38mph and shifts into 3rd gear straight from first...after some highway driving the tranny seems to function completely normally.

Anyone have any ideas?

Thanks,
Aaron Riesbeck

 

[Airhead315]

noone can help me? please? heh dont make me beg....

 

[MrShorty]

My thought: vacuum leak. A vacuum leak will cause a high idle, and a vacuum leak in the line between the engine and the transmission will make the transmission think you are at WOT and not want to upshift.

 

[410Fortune]

I agree, check all the vacuum lines for a leak. This has been covered on these forums and a search should result in many places and ways to check.

the earlier trucks like yours are notorious for leaking at the lower intake manifold.

High idle = vacuum leak, most of the time.
Let us know what you find!!

 

[Opera House]

On my 92, removing the electrical connector to the IAC will make it stall. That means you have a really big leak or the throttle body is sticking open tat causes the computer to turn the IAC off. Check for a missing cap on the vacuum tree (back drivers side).

A late 1>2 shift is often causes by a sticking speed governor in the extension housing of the transmission (you can get to it). The 1>3 shift sounds like a broken band, but that doesn't recover. See if you can drive in manual 2. Over reving can be causes by a bad TPS, but that only opens the IAC and you say that isn't working.

 

[410Fortune]

I dont think the IAC andf TPS are sending signals when the truck is in closed loop still or at WOT? Right?

 

[MazdaGreg]

Just as a FYI, i had a similar problem with my Navajo. idled about 1500 or so, and could not find a vacuum leak anywhere. So i started tracing the entire vaccum system, and discovered a bad PCV Valve. Double check that in your diagnosis. It's a pretty big leak when it does go, and you can't hear it either. It also made it hard to start in the mornings. Don't know about the tranny issue, mine is a 5spd.

Keep us posted.