Someone help me with this high idle problem, please! I apologize for this long posting, but I want to let you know what was tried, before you suggest.
My '91 Explorer 4x4 XLT 4.0L pushrod engine, w/ A04D trans has high idle most of the time. Engine has 133k miles. Idle usually ranges 11K - 12K, sometimes 18k, in Park or Neutral. In Drive foot on brake @ stoplight is 800 rpm. The problem started a couple of years ago, & was quite rare, then be OK after just a little while, usually. After having the RH engine head replaced, the high idle is almost always there. The head was R & R because middle exhaust valve worked out of head causing valve to contact piston & bend valve, cracking head. Only 20 months & 8 - 10K miles after complete valve job, replacing the LH engine head due to hole melted in middle exhaust valve.
Replaced IAC, MAF, TPS. An independent shop then also checked codes, vacuum leaks, TPS, IAC, you name it. Took it to Ford & checked all the same stuff. The tech claimed he could block the intake with his hand, the engine would not change speed. They claim the Ford Service Hotline points to intake leak, possibly @ an injector or bad lower intake. The injectors were never removed, but I pulled every gasket & seal for injectors, fuel rail, intake, throttle body, carefully checked all, & put in new gaskets, seals, etc. I replaced the temp sensor for the computer (the one with a 2-wire harness).
The dash temp guage shows only normal temp, with engine warming up in normal time. After replacing all the seals mentioned above, I tried the hand in front of the throttle body like the Ford tech, & thought I was going to have it sucked in. The engine almost stalled, so I it does not seem like a leak, but disconnecting the wire to the IAC does not affect the idle. What gives???
This is getting hard on brakes & fuel. With gas prices the way they are going, any help would be greatly appreciated.

 

Hey, anybody know anything about this? After replacing all the gaskets & seals, I find the tranny not wanting to shift up when cold. But when first starting out in the morning, when shifting into Rev. the computer kicks the idle up to 12K BEFORE the transmission even has a chance to lock up. The racing engine problem seems connected to the tranny, whether bad electrical connection, faulty tranny solenoid, or computer.
Anyone got a suggestion where to start?
Right now it's at the tranny shop that rebuilt it 11k miles ago.
Thanks

 

I feel for you. I have a 97 Ford Explorer. 4.0 v6 sohc. sounds like almost the same thing. I posted a new thread today for first time and I am waiting on an answer. A couple weeks ago mine stalled. It has always idled under 1000 and it seems ok to me but what do I know, I'm a girl. Then, the other day, it raced up to almost 2000rpms and wouldn't drop. Yesterday, I drove it into town and it raced at all stops around 2000 rpms. Kinda hard to keep it from drifting. I'm not used to holding down the brake that hard. And I also don't trust the brakes anymore but God! that's another problem (I think mechanic damaged damaged ABS wheeel sensor when he replace lower ball joints). Anyhow, ever since this high idling thing started, I don't know if this is part of this problem or another problem with something else, but also, yesterday, I was going around a sharp turn on a side road, and I went from 40mph to around 20mph. When I gave it gas again to get back up to my higher speed, it started choking, or something. I did find an AWESOME thread by some wolfman or something like that. It says about IAC or idling in the subject line. Check it out. Very thorough.

 

It sounds like a problem with the vaccum modulator. It controls the when the tranny shifts and is controled by engine vaccum. That is about the only thing i can think of that could affect the engine and the tranny at the same time.

Chris

 

OK. I got it back after the tranny shop gave it a check up, and they say everything on the tranny (solenoids, wiring, modulator, clutches, etc.) ALL check out OK. The codes are showing #12 & #13, for bad high idle & bad curb idle. The IAC,TPS, MAF, O2 sensors are all new. It seems like a computer problem (PCM), because after startup, if it idles OK, the idle jumps when shifting from P or N into gear. Especially into Reverse to back out of the garage in the AM. The rpm jump happens so quickly when moving the shift lever, it jumps even before the tranny can start to lock up. That would seem to indicate that the PCM is telling the IAC to stay open more to bump the idle up. With the tranny in gear, and foot on brake rpm is about 800. Can you tell me where to go to find a "decision tree" to chase down the cause for these? That's all the dealer will do. The chart in my Haynes manual does not go very far for this, and my Chilton's is even worse.

I'm about ready to go to NAPA to get a new PCM for $125. Ford is $300, but I can get it at jobber cost, hopefullly for less. Does anyone know about if aftermarket is OK for this? I forgot to ask Napa what brand theirs is.

Thanks

 

After taking it back to FORD for a re-diagnose, they determined that it is a worn throttle body not closing properly. The tech confirmed this by testing with one from another vehicle. That actually makes more sense, given all of the symptoms, since the rpms would quite often come back down to normal with a VERY quick jab of the gas pedal. Has anyone seen where the throttle body shaft was worn like that?
I will let you know next week, as it will be Friday before the TB comes in, and I plan to take it out of town for the holiday weekend.

 

I understand that's one of the reasons to periodically spray the throttle body inlet flapper valve (both sides). Truck runs good, cleans the shaft and how it fits in the body.

 

Okaaaaayyyyyyy! Ford finally, properly diagnosed the problem. The throttle body was indeed worn. If I only knew at the time what a new should look like, I might have diagnosed it myself!
There was at least 1/64" space on one side of the butterfly. Spring pressure caused it to always be against the side opposite the TPS. In addition to the butterfly being worn, the bore was worn where the butterfly stopped against it, leaving a nasty ridge 1/4 way around on front & a matching one 1/4 way around on back side of butterfly. I'm guessing that the "mechanic" who replaced the bad engine head & thoughtfully cleaned the TB, had adjusted the stop screw. Or perhaps cleaning it allowed the flap to ride further to the side under spring pressure, and nearly always catch on the ridge. I'm jot sure which, maybe it was both.
I suppose if I had re-adjusted the stop it might have worked for a while, but with such a gap, too much air was definitely getting by. The new one, and it's a FORD only part, has virtually NO gap around the butterfly. It works the way it should. For Memorial weekend I took the truck from the 100 degree heat of Phoenix up North to the mountains pulling a large pop-up tent trailer, and the tired old Explorer did pretty good.
This should be the end of this posting for me.
Thanks for all the help & suggestions you folks sent me.
Since the new camper is probably more than I should pull up those mountains, I'll probably see if I can afford a newer, larger vehicle sometime in the next year. Oh joy of joys!