Monday I started my truck to drive home and when it started it did what sounded like a backfire in the carb and died. It was like it rec'd too much gas. I didn't give it hardly any. Anyway I turned the key and it fired up just fine. Then on the drive home the engine started idling high around 1600 rpm. Now it is a constant high idle.

I went right to the engine and disconnected the pos cable and left off for 10 min, then turned key on and let it idle for 5 min. At first it sounded like the it was going to idle down, but after about 15 seconds it went back up. This morning I pulled my air filter and checked it. Looked for vaccuum leaks, gave the MAf a wipe down inside. Took pos cable off for 15 min, then idled for 5 min. It immediately went back to high idle showing no signs of dropping down.

I have been reading many posts but just want to make sure I have all that I need to check. IAC check, Vaccuum leaks, MAF clean, and possibly thermostat. My temp has been fine. Any other obvious things to look at.

I did just have a custom exhaust put on last week. Single in dual out flowmaster 40. Plugs and wires are new as of June, as well as air filter.

Any ideas on what this is!?

And see if it stops. I have an unusual failure in my 92. The computer was driving the IAC open. It started out doing that only on long trips, then more often. I actually built a current source that bypassed the computer and gave me a high idle when cold then switched to a lower speed when warm. Car has been off the road for a while till I rebuild the transmision. Have to tackel that problem next month.

how cold is it when you crank it? when the engine is cold it idles higher to warm itself up and stays that way till the temp guage reads a little above the "cold." to completely redo my computer i had to let the car sit with the battery unplugged overnight, then i started it up and let it sit for about 5 minutes to reprogram itself. some people only need to disengage the battery for 2 mins, but for me i let it sit for 10 and it didn't flash the computer so i said the heck with it and left it overnight. hope it's as simple as that. good luck.

You could also just check that the throttle cable is not stuck/frayed. But I bet its the IAC they seem to go quite often.

Well thanks all,

I tried to reset the computer after driving home from work about 45 miles so I know the engine was warm. This morning it was about 46 when I tried to reset it and the car had not been started since the previous day. I may give it the overnight try supposed to be 48-50 tomorrow.

I'll try to unplug the IAC today and see what it does. If I unplug the IAC and the idle comes back down, can I leave it unplugged for a while? I would imagine it would be hard starting with the IAC unplugged. Come to think of it the truck has been slow starting these past few months.

I'll just steal the IAC off my wife's 94 Explorer. She'll never notice it. Her's is an automatic and mine's a manual. She drives a mile to work. I drive 45 miles.

Oh the cable is not frayed or stuck. Very first thing I checked. You know stomped on the gas pedal a few times to loosen it if stuck. Hey it works, low tech ya know!!

Sometimes you just can't see the wood for the trees! Just a thought and I'm not sure but there is a IAT (Intake Air Temp) sensor. Not sure how you test it though and I think it would give you a CEL so perhaps not. But you never know. All the best.

"would give you a CEL so perhaps"


What is a CEL?

The engine will not run when it is cold and you take your foot off the gas. Even when it is warm, the engine will idle at about 400 rpm at best.

Sorry CEL (Check Engine Light) IE: there should be a code to read.

I bought a code reader last summer for a trip to Oregon, but as of yet I haven't used it. I wanted to make sure that I understood how to read the lights before I used it. Maybe its time to break out the instructions and give it a go.

I unplugged my IAC yesterday while the engine was running and it made no difference in the idle.

I do have a question for anyone to answer.

1. Why wouldn't my check engine light come on with this problem?

2. There are two sensors or valves on the manifold, one is the IAC what is the other, right next to the protective cover over the throttle cable?

"IAT"

Where is the IAT located 91-94?

I am at a loss for what to check next. Hopefully I will know more tonight after I use my code reader. I'll post the codes I pull if interested.

Lets get them codes it should give us a clue.
The IAT is located in the air intake pipe just after the MAF. So you got air filter then MAF then IAT. But it would give a code if faulty.
When you unpluged the IAC valve and nothing happened this could well indicate that it is stuck open. Because the IAC valve controls the amount of air to bypass the throttle plate when the throttle valve is closed or at idle position. Thus effecting the idle speed. All the best. Look forward to the codes.:D

I didn't remove the valve to see if it was stuck open. I will tonight. I think there was a thread I found earlier on the removal and cleaning of the IAC. I'll print it out.

Ok well the code reader didn't go as well as I had planned! I will have to retry today.

This is what I got from the code reader:

1st code --- 2nd code --- 1st code
52------------- 2------------- 111

This was from the KOEO test. The codes make no sense to me.

I pulled my IAC and cleaned it. It didn't appear to be stuck open and the plunger moved freely. It was really dirty lots of carbon build-up. Unfortunately the Idle is still really high. When shifting and engaging the clutch the idle may go as high as 2300 rpm then drop down to 1600 rpm.

I read a post where someone had a similar problem and the answer was the thermostat. Does this sound plausible to anyone? I looked into the engine compartment and shook my head as I found the thermostat buried under hoses and brackets. Looks like no fun to pull out and check!!

I know you said you looked for a vacuum leak, but with a backfire one of the vacuum caps on the tee at the back of the engine may have popped off, I would check them again, check the brake booster, and on a long shot, the backfire may have damaged the intake gasket.

If your IAC is carbon fouled clean it AND the Throttle Body while you are checking everything out.

Good Luck

Try running the codes again, 91 codes are 2 digits might the codes be

52 21 11

21 is IAT out of range - its on the intake between the vacuum tee and the IAC valve

11 is PASS

52 is not recognized on 91s

This is speculation, but the codes are close to what you posted- its hard to count beeps, flashes ,etc depending on the scanner.

I'll check my codes again and also check the IAT.

I looked in my code book and code 21 is "Cooloing temp sensor out of specified range or ECT out of range"

I need to find a Chilton's, looked for one yesterday no one had one. I found a Navajo one but kept looking for the Explorer book. Where is the intake gasket located? I swear I can hear a significant difference in air flow in the engine. Makes a deep air sucking sound. I also have heard the humming which I thought was an indicator of the IAC needing to be replaced.

I just wanted to add that the backfire I mentioned wasn't a true hard backfire, but a puff. Sounded more like air than bang.

Just for further understanding what did you mean by code 52 is not recognized for 91's. My code book says something about power steering pressure switch open.

Are you saying this is an incorrect fault code? My understanding is that I need to clear the KOEO codes before I can run the KOER test. Which I can't run until I run the timing test. So actually I may never do the engine running test since I have no timing light.

Its not recognized because the 91s dont have one.

If you are hearing hisssing I would very carefully check the vacuum tee at the rear- it has to have caps or hoses on all of the nipples.

You are right I miss read the 21 code ECT out of self test range. ECT should be at .61 volts at op temp-(194deg) , resistance 2.80 K ohms, cold resistance 37.30K ohms @ 68 deg

The KOEO codes are followed by a seperator and then the continuous memory codes are displayed. Since you disconnected ythe battery the continuous memory codes are washed- hence the 11 or OK code

Recheck the KOEO codes

1/2 second between flashes for digits, 2 seconds between digits,a dn 4 seconds between codes, you should have a single pulse 6-9 sec after the KOEO codes and then after another 6-9 sec the Continuous Memory codes are displayed.


Hope that helps a bit

Problem was I was not looking at the reader rather listening to the beeps as I wrote them down. It was my first time using the code reader.

Somewhere else on here I read that this could be as simple as replacing my Thermostat. That's what fixed their problem. What relationship would these two things have? Obviously measuring the coolant temp is what the ECT does but if stuck closed how would that affect the engine idle. I am suspecting something along these lines as I noticed my temp gauge, which I rarely notice, was kind of bouncing this morning.

If the stat is stuck open the engine wont get to operating temp, and the comp will keep the engine in the "warm up " mode. Higher idle, rich mix.

Dang I may end up having to check the T-stat as well. And it seems to be well buried in the front of the engine.

I am going to get the codes read again at lunch time which is now.

Well back I went into my engine compartment at lunch time and found my problem. Thanks for all the help I don't know what I would do without this message board.

It's so helpful. It keeps me company when I'm alone with nothing to do. It's a mistress to some and a wife to others. Heck if it weren't for my Ford Explorer I'd be all alone!

Ha, ha, ha, ha!! Thanks all!

A vacuum cap? What?

May help others who have a similar problem.

Since you pulled some codes I would follow up with them, even if the immediate problem is solved.

Glad you found ????? the problem.

Originally posted by SteveVB
A vacuum cap? What?

May help others who have a similar problem.

Since you pulled some codes I would follow up with them, even if the immediate problem is solved.

Glad you found ????? the problem.

I second that. I think that a hose or cap was missing from the intake manifold, but it would be nice to confirm this for others who might have the same symptoms.

Hey Jack
Do please tell us what was the problem:confused:
Was it a vacuum pipe/cap?

I Went back at lunch time to go through the engine better. I had checked for vaccuum caps when the engine was off previously. I had checked the vaccuum lines with the engine running, but I was focused on the lines.

I went back and found that the rear most cap had blown off. I removed a valve stem cap from my tire and managed to get it over the vaccuum nipple and my idle came roaring back down.

I then looked around on the ground under my truck and there was the missing vaccuum cap.

I felt so ridiculous. But on a good note, my wife's Explorer has a rough idle and now I feel confident I know all the items to check and what to look for.

Jack don't feel bad it happens to us all at one time or another. With these modern emmision control engines it is so easy to fear the worst that we overlook the obvious. Best of luck with the wifes x that will be much harder (serious critic involved):D :D :D