92 really high idle...

Black Frog · Apr 11, 2011

I have a 92 Ranger (488k miles!) has a really high idle. I mean really high, like 3000 rpm. Just started doing this yesterday . Doesn't matter if the engine is warm or cold.

If I pull the iac connector, should the engine shut off ? Or is this a tps problem most likely?

Black Frog · Apr 11, 2011

...and a little more info- It doesn't fluctuate much from that 3000rpm value after a long drive or starting cold. And it just started doing it out of nowhere, so I'm thinking that it probably isn't a vaccuum leak since it was so sudden and drastic. Seems to me more like component failure?

Black Frog · Apr 11, 2011

ok- a little more info. I can unplug the TPS sensor, and there is no change in the 3000 rpm idle.

Reconnect the TPS, and unplug the IAC solenoid, and it throttles down to barely running at idle. BIG change.

But I'm unsure if that is telling me that the IAC or TPS is good or bad?

Black Frog · Apr 11, 2011

Installed a new TPS, no change. Measured the resistance across the terminals of the IAC solenoid, about 10.6 ohms.

When I unplug the IAC, it barely idles. When it is connected I get my 3000rpm idle from startup. So now I'm thinking that the IAC works ok, and is being told to open up letting all that air in. And since it barely idles with the IAC unplugged, I'm guessing that vacuum leaks are not my problem.

Starting to lean towards the MAF? ...hoping it's not the computer.

Big Jim M · Apr 11, 2011

I'd start by giving the maf and iac a good cleaning and work from there.
Big JIm

bhawk · Apr 11, 2011

I'd do a thorough inspection of every vacuum line and fitting. If a hose deteriorates all of a sudden it will allow air in. There is one vacuum line that connects with a plastic T under the throttle body, just above the temp sensor. It runs to the charcoal vacuum canister under the air conditioner compressor. There are at least 2 vacuum lines coming off a fitting at the rear of the upper intake manifold. Then there is the power brake booster vacuum line going from the same fitting to the power brake booster. I'd look at the fitting on the upper intake real close. I had mine off a few weeks ago and that fitting was quite rusted behind where you can't see it well. Look with a mirror, the fitting could have rusted thru and exposed a hole. There is also a vacuum line running to the fuel pressure regulator also, make sure it is tight and no leaking. Those are the lines I can remember.
Anyway, we had a high idle on our 94. Started up and idled at 3000, then very slowly lowered to 1200 or 1150 at the lowest. I tried everything. New tps, new maf, new IAC, sprayed all my vacuum lines down with propane, could not find any leaks. So, I bit the bullet and replaced the lower intake manifold gasket. Bingo, problem solved. it starts at 1200 or so, and idles down to 650 hot. Real nice. If your problem persists for a few weeks, pull all you spark plugs to see if they are burning white, which confirms a lean mixture, or too much air.

Black Frog · Apr 11, 2011

thanks for the input.

Tried a new MAF- still no change. I can see the IAC solenoid engaging as soon as the key is put to the "on" position. So it is moving to the full-open solenoid state from a closed state. That tells me that the IAC is probably fine since if I unplug it, the solenoid closes and cuts off the incoming air and it idles right down.

Bhawk- The difference I see with your situation is that my truck idles at 3k rpm ALL the time. It never idles down, even after an hour drive. And it never varies from that 3k mark which sort of leads me to think it is an electronic problem somewhere instead of a leak. And it came out of nowhere, it was fine one day and then the next time I started it up it was 3k idle.

But I'll give the vacuum lines a good once-over and see if I can find anything....

Big Jim M · Apr 11, 2011

question

Black Frog said:
thanks for the input.

Tried a new MAF- still no change. I can see the IAC solenoid engaging as soon as the key is put to the "on" position. So it is moving to the full-open solenoid state from a closed state. That tells me that the IAC is probably fine since if I unplug it, the solenoid closes and cuts off the incoming air and it idles right down.

Bhawk- The difference I see with your situation is that my truck idles at 3k rpm ALL the time. It never idles down, even after an hour drive. And it never varies from that 3k mark which sort of leads me to think it is an electronic problem somewhere instead of a leak. And it came out of nowhere, it was fine one day and then the next time I started it up it was 3k idle.

But I'll give the vacuum lines a good once-over and see if I can find anything....

So if the iac is unplugged it will idle fine? Then doesn't that eleminate a vac leak? For sure I'd be trying another iac.
Big JIm :hottubfun:

bhawk · Apr 11, 2011

On our ranger, when we unplugged the IAC, it did idle down alot, to say 800. But, you couldn't drive away like that, it seemed to buck a bit, ran erratic off the idle. So, we plugged it back in and did all the other replacements and ultimately found it was the lower intake gasket. So, I would say that just because you get a lower idle with the IAC unplugged, it does not eliminate a vacuum leak. The real problem with a vacuum leak is that the intake seals to the cylinder heads UNDER the valve covers, so no amount of propane or starter fluids will get there so you won't find that leak with sprays. Gotta take the upper off and at least check the torque on the lower intake bolts. In our case, I could unscrew all 8 bolts holding the lower intake down with one hand. They were loose. Maybe if you just take your upper intake off and re-torque all 8 hold down bolts, you might seal it up.

Black Frog · Apr 12, 2011

Big Jim M said:
So if the iac is unplugged it will idle fine? Then doesn't that eleminate a vac leak? For sure I'd be trying another iac.

Well it idles WAY down if you unplug the IAC.. down below the normal idle point, almost to where it won't stay running.

Does that IAC just have two postions of operation? Open/Closed? Or does it have a variable state depending on the voltage going to the solenoid?

yorxs · May 15, 2011

Black Frog said:
I have a 92 Ranger (488k miles!) has a really high idle. I mean really high, like 3000 rpm. Just started doing this yesterday . Doesn't matter if the engine is warm or cold.

If I pull the iac connector, should the engine shut off ? Or is this a tps problem most likely?

I had the exact same problem, 2500 rpm no matter if it was warm or cold. Took the IAC off and watched it as some one else turned the ignition on and off. I could see that the IAC was not fully actuating open and closed, so I sprayed it with WD40 and it began to fully actuate fully. When I reattached to the truck, it began to idle at about 700 rpms again.

Black Frog · May 16, 2011

Glad your problem was an easy fix... Mine turned out to be a little more involved once my tach stopped working, and then a few weeks later I had intermittent engine power loss.

Detailed in this thread:

http://www.therangerstation.com/forums/showthread.php?t=108091

All is good now, and 500k is in sight!

parson2008 · May 17, 2011

mine did the same... lower intake gasket

Hellcat · May 17, 2011

I had the same symptoms turned out to be a bad 02 sensor. I looked and looked before finding it. The OBT 1 makes it hard to get good reading unless you have a GOOD scanner

holyford86 · May 17, 2011

with it idling down once the IAC is unplugged seems to tell me that the IAC is junk. TPS and MAF have no bearing on idle (you can unplug both of them and the engine will still start).

92 really high idle...

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