High idle causes?
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Mountain Pass
Joined: Mar 2008
Posts: 163
Likes: 37
From: SW GA
High idle causes?
So I rescued this little '91 2.3l, 5spn reg cab xlt. Most folks would have passed but I needed a back-up ride while working on engine of my daily driver. Well I'm in about a grand total for tires front calipers, battery, timing belt and a junkyard 3g alternator and some new fuel injectors after cleaning the fuel tank and installing new pump. I finally got the idle down from 1600 to 11-1200 with coolant temp sensor, cleaning iac and maf. I checked the hoses and such looking for a vacuum leak but nothing. Only thing I haven't checked is brake booster but I don't hear any hissing nor are brakes hard. I'm at a loss at this point. Fuel pressure is 45psi, new pressure regulator. Only idea I have is computer. It is driven on road at 60mph for 125miles per day so it is only annoying me when in town or as I park. The power steering pressure switch change mad a 400rpm drop once changed. If I could get it 800 I would be happy. Oh mileage is about 19 so something is calling for enrichment I just haven't found it yet.
Fleet Mechanic
Joined: Jun 2023
Posts: 1,357
Likes: 377
From: WA
Looks like it has the usual Ford IAC valve. If you unplug it it should close completely and give the lowest idle RPM possible. If unplugging it doesn't drop idle RPM then it's not a computer problem, at least as far as computer-controlled idle speed. A simple way to get closer.
https://www.rockauto.com/en/catalog/...ac)+valve,6072
https://www.rockauto.com/en/catalog/...ac)+valve,6072
Thread Starter
|
Mountain Pass
Joined: Mar 2008
Posts: 163
Likes: 37
From: SW GA
Looks like it has the usual Ford IAC valve. If you unplug it it should close completely and give the lowest idle RPM possible. If unplugging it doesn't drop idle RPM then it's not a computer problem, at least as far as computer-controlled idle speed. A simple way to get closer.
https://www.rockauto.com/en/catalog/...ac)+valve,6072
https://www.rockauto.com/en/catalog/...ac)+valve,6072
Fleet Mechanic
Joined: Jun 2023
Posts: 1,357
Likes: 377
From: WA
Check all of the hoses connected to the intake manifold. And the PCV system, the hose from the valve cover. The PCV system is connected to the intake manifold. Sounds like you have a leak of air in to the intake system somewhere. It doesn't take much to raise the idle speed.
Thread Starter
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Mountain Pass
Joined: Mar 2008
Posts: 163
Likes: 37
From: SW GA
Check all of the hoses connected to the intake manifold. And the PCV system, the hose from the valve cover. The PCV system is connected to the intake manifold. Sounds like you have a leak of air in to the intake system somewhere. It doesn't take much to raise the idle speed.
Hotshot
Joined: Jun 2015
Posts: 12,786
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^^ This is the problem ^^
5th Wheeling
Joined: Jul 2025
Posts: 44
Likes: 7
[QUOTE=generalee;21727172]Drove couple of days w/ both iac and maf unplugged to no avail. Maybe I disconnect battery one last time and see if the reset
will get cobwebs or whatever out. Thanks![/
QUOTE]
Have you considered the base idle may have been tampered with?
will get cobwebs or whatever out. Thanks![/
QUOTE]
Have you considered the base idle may have been tampered with?
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Mountain Pass
Joined: Mar 2008
Posts: 163
Likes: 37
From: SW GA
New iac, removed throttlebody and replaced tps. Reset everything and now while it is very clod outside it starts and idles at a calm 1000 rpm. After driving a bit it goes back to idling at 1500-1600. I know the coolant temp sensor is likely the issue as the connectors are prone to poor connection from corrosion or pin misalignment. If this doesn't help I'm bringing out the hammer or cramming a wool sock down the intake tube.
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Fleet Mechanic
Joined: Jun 2023
Posts: 1,357
Likes: 377
From: WA
Looks like it has the usual Ford IAC valve. If you unplug it it should close completely and give the lowest idle RPM possible. If unplugging it doesn't drop idle RPM then it's not a computer problem, at least as far as computer-controlled idle speed. A simple way to get closer.
https://www.rockauto.com/en/catalog/...ac)+valve,6072
https://www.rockauto.com/en/catalog/...ac)+valve,6072
If idle speed doesn't drop when unplugging the IACV then it's not the computer controlling idle. Try pushing the throttle blade closed by hand. Maybe you have a gummed up throttle blade. I had an older car that used to get a sticky throttle after warming up. It was a gummed up blade. Could even be a weak throttle return spring.
Thread Starter
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Mountain Pass
Joined: Mar 2008
Posts: 163
Likes: 37
From: SW GA
Throttle body has been removed, cleaned and returned to service w/ new gasket. Throttle stop was shortened a little and little effect. Took the ect sensor out (what a PITA) and hooked it up to my multimeter and seemed ok at ambient but a quick hit from my map touch and it became obvious it was going the wrong way on resistance. New one installed and at first it started idling at 1000 rpm. Great till it warms a little and back up to 1500-1800. At least it runs better and check engine light doesn't come on most of the time and sometimes it goes back out. I am going to disconnect every vacuum line and plug them and one at a time re-connect until I find culprit. I still don't understand the power steering fault or open circuit as the code says. I checked the ground side to battery and have continuity. The power side only registers 8.5 volts not 12. I would have guessed 5v or 12v. None of the harness looks buggered. Mystery
Thread Starter
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Mountain Pass
Joined: Mar 2008
Posts: 163
Likes: 37
From: SW GA
Seems my new tps is a source. It has a little tension when installed and the output voltage at idle is 1.03v. I slotted the sensor then used only 1 mounting screw to maximize the rotation to relieve the tension in sensor . Now the max idle is about 1300-1400. Runs some better and not racing like it was at Daytona. Gotta figure a different attachment that allows more rotation. Sensor may be faulty but I don't want the hassle of returning after I have worked it with the dremel.
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