1992 Ranger - Racing Engine Upon Startup?

[rangerenthiusiast]

So when my ’92 Ranger 4.0 first starts up, the idle races, then drops off, races, then drops off... and on and on it goes. Anyone know what causes this?

I recently replaced the MAF unit and sensor with a rebuild, but I can’t remember if it was doing it beforehand or not (I bought the truck recently and had a bunch of problems early on, so my memory’s not too clear).

Thanks.

 

[shadetreebronco]

A bad Idle air controller was my problem . You can clean them with carb cleaner .
Mine had no gasket but was red hot.
A new one fixed it .

 

[rangerenthiusiast]

A bad Idle air controller was my problem . You can clean them with carb cleaner .
Mine had no gasket but was red hot.
A new one fixed it .

I’m not sure where that’s located. Are you referring to the Mass Air Flow Meter? I just replaced that whole unit, including the sensor.

 

[shadetreebronco]

On my 87 2.9 its on the passenger side of the upper air intake manifold , on my 96 4.0 its on the drivers side upper air intake manifold.
I suggest doing a search here to find out more about diagnosing that problem .
Lots of info here.

 

[rangerenthiusiast]

I’ll look into it. Got a few other ideas while I was looking it up as well.

 

[rangerenthiusiast]

A bad Idle air controller was my problem . You can clean them with carb cleaner .
Mine had no gasket but was red hot.
A new one fixed it .

So I looked into what this was, then took it off and cleaned the insides with some carb cleaner today while I was doing other things on the truck. Put it back on the truck and noticed no difference. While it was idling, I disconnected the wiring harness from the idle controller and noticed no difference at all (it was idling at about 1K, which is the low end of where it idles, before it jumps up to 1300 RPMs). Took her for a test run, then parked and noticed that she was idling much higher than usual (about 1700 RPMs). Pulled the plug on the idle controller again and they dropped down to 1K. Not sure if this means it’s working intermittently or if there’s a different issue to address.

To further complicate things, I also noticed that every time the idle shoots up, the AC compressor clutch engages for a few seconds, even though the AC button is not on inside the cab. The line coming off of it is also ice cold. Does anyone know if this is related or a separate problem?

Could really use a hand here. It’s driving me nuts.

 

[rusty ol ranger]

Well...

First off its not a good idea to use carb cleaner on anything intake plenium related. It eats off special coatings.

Secondly, alot of times idle air controllers need to just be replaced, sometimes cleaning works, but usually not.

Thirdly, i wonder if the WOT A/C cut off relay is bad? I know 1st gens had these, not sure about yours.

Fourthly, have you checked for vaccum leaks?

 

[rangerenthiusiast]

Well...

First off its not a good idea to use carb cleaner on anything intake plenium related. It eats off special coatings.

Secondly, alot of times idle air controllers need to just be replaced, sometimes cleaning works, but usually not.

Thirdly, i wonder if the WOT A/C cut off relay is bad? I know 1st gens had these, not sure about yours.

Fourthly, have you checked for vaccum leaks?

Hey, Rusty.

The carb cleaner note seems a bit odd, given how many people (both here and on youtube) recommended it for cleaning both the IAC and the plenum. Not stating that they’re right, just that a lot of them are saying it. Didn’t realize there were special coatings inside the plenum, but after 26 years, would they even still exist?

I could totally believe that the IAC needs to be replaced. When I had it out, I was able to actuate the inner shaft pretty easily, but it was also badly corroded, which leads me to believe that, like so many things on this truck, it’s the original (especially since it’s Motorcraft). I’ll hunt around and see if there’s a way to test it.

The WOT AC cut off relay is a good thought and I could also see where problems with it could be related to a bad IAC. I guess that my real question here is, regardless of what’s causing it to turn on and cut off the way it does, should the AC pump clutch be engaging at all if the AC button is not on in the cab?

Vacuum leaks are definitely on my list to check for. I’ve poked around a bit under the hood looking for disconnected or broken lines, but haven’t come up with anything other than a few connectors on the vacuum block that were capped off in the past by someone. Still deciding if I want to buy/build a smoke machine or try using a pressure gauge on the vacuum booster hose. Still researching these.

 

[rusty ol ranger]

I believe it says right on the back of carb cleaner not to use it on TBs/pleniums , of course maybe theyve changed it in recent years, i havent read the back of a can in years.

A/C compressors will cycle if the defrost is on, atleast on newer stuff. But other then that no i dont believe it should cycle.

I believe the CPU compensates idle (ups it) when the A/C is on, so it may be the AC issue causing the idle problems

Just for poo and giggles try unplugging the AC compressor, see if that calms things down

 

[rangerenthiusiast]

I believe it says right on the back of carb cleaner not to use it on TBs/pleniums , of course maybe theyve changed it in recent years, i havent read the back of a can in years.

A/C compressors will cycle if the defrost is on, atleast on newer stuff. But other then that no i dont believe it should cycle.

I believe the CPU compensates idle (ups it) when the A/C is on, so it may be the AC issue causing the idle problems

Just for poo and giggles try unplugging the AC compressor, see if that calms things down

Well, when you’re right, you’re right. Looked on the back of the can of carb cleaner and buried halfway down the lines of gibberish that I never read, it clearly states that it’s “not recommended for fuel injected vehicles.” So there’s that.

Went out to test a few of your theories before running errands today. Moved the climate controls from defroster to floor and disconnected the power to the AC compressor pump (breaking the plastic retaining clip in the process, of course). Started her up and she idled right at 800-900 RPMs, just like she should (instead of the 1300-1700 that she had been). Plugged the AC back in and everything stayed fine, with the clutch no longer cycling on and off like before. But by the time I reach the first stop sign a few miles away, she was back to idling at 17K.

While I was in the parking lot at the laundromat, I disconnected the AIC wires and she went back down to 800-900. With the IAC disabled, I drove the truck home and noticed several improvements. She shifted a little sooner (a good thing) and much smoother. The problem I’ve been having with her kicking down through several gears at the last minute (10-20 feet) when I pulled up to a stop sign was also taken care of. I thought, “Great! I’ll just pick up a new IAC and at least this problem will be solved!” Then I pulled into the driveway and the idle started out at 15K, before slowly dropping down to 13K and bouncing between 11K and 13K before shutting her down.

So I’m thinking that maybe the IAC is bad, but I have an additional vacuum leak somewhere. Either that, or this truck somehow needs the IAC to idle properly when warm, but not when cold. Anyone have any thoughts on this? If I do have to replace the IAC, I’m thinking about buying this Hitachi one from Advance: https://shop.advanceautoparts.com/p/hitachi-idle-air-control-valve-abv0033/10594937-P?searchTerm=Idle+Air+Controller

I know it’s not a Motorcraft, but it’s about half the price and I just have so many other parts to buy for this truck. Anyone bought one before?

Thanks!

 

[rusty ol ranger]

If your truck is idling at 11-14k you shoulda sent a rod into orbit (just kidding, i know you meant 1100-1400)

I would replace the idle air first, its cheap, its easy, and see if that fixes it before i dived to deep.

I *think* if you unplug the idle air when warm it should rev higher, because the CPU uses the tps to compensate, but im not sure on that fact.

As far as a hitachi IAC, an IAC is an IAC, its not like an oil pump, if it fails in 6 months, just get a good one, no harm done.

 

[rangerenthiusiast]

If your truck is idling at 11-14k you shoulda sent a rod into orbit (just kidding, i know you meant 1100-1400)

I would replace the idle air first, its cheap, its easy, and see if that fixes it before i dived to deep.

I *think* if you unplug the idle air when warm it should rev higher, because the CPU uses the tps to compensate, but im not sure on that fact.

As far as a hitachi IAC, an IAC is an IAC, its not like an oil pump, if it fails in 6 months, just get a good one, no harm done.

Hahahahahahah! Jeez, sometimes I surprise myself with my own idiocy. Did I not mention that my Ranger was built by NASA? lol

Hmmmm... odd, because when I unplug mine, the idle kicks down. Which is a relief, because when it’s idling around 1700, she sounds like she’s gonna blow. Not sure what the tps is, though...

Thanks for your opinion on the Hitachi. I’m buying that sucker. tonight It’s getting to the point (which I’ve been trying to avoid), where I just start throwing parts at this baby.

 

[rusty ol ranger]

TPS- Throttle position sensor

Im a carburator man, but sometimes i can piss my way thru EFI, hopefully someone stops by whos much better with this new fangled shit

 

[rangerenthiusiast]

TPS- Throttle position sensor

Im a carburator man, but sometimes i can piss my way thru EFI, hopefully someone stops by whos much better with this new fangled shit

Oh, man. Just ordered the IAC; hope the TPS isn’t bad too. When I bought this truck, I had really been wanting a 78-79 F100 or the like, but they’re rare as hen’s teeth up here in the NoEast. When you do find one that’s not totally rotted out, people want an absolute fortune for them (which seems bizarre, since I grew up in them and they were one of the cheapest vehicles you could buy at the time).

I knew that a ’92 Ranger would still have some modern crap in it, but I was hoping it would still be a lot more basic than my 2000 Jetta. Sure seems like there are a lot of sensors and other doo-hickeys to worry about. Sigh. At least I have a truck again, and a Ford at that. I’ll deal with it, thanks in large part to all the help I’m getting from the good folks here on the forum.

 

[rusty ol ranger]

Nah, Rangers are pretty simple trucks. At least you have some room to work and parts are cheap.

73-79 Fords will always be my automotive love affair. But the supply of affordable, unmolested, daily driver/work grade trucks are drying up quick. You either have trailer queen show trucks or purpose built rigs.

Funny thing is, 73-79, and 92-96 trucks, espicially nice clean 4wds, seem to be gaining value pretty quickly. I remember even 10-15 years ago you could barely give them away