High idle problem with 5.0L HO engine

I have a 91 TBird with the 5.0L HO engine and AOD. It suddenly developed a high idle. I checked the linkage, nothing is binding or hanging up. I even unhooked all the cables from the throttle body, made sure it was closed and started it. High idle.
It idles about 2000 rpm. At first it would only idle high a few seconds when you first started it up. Now it idles high, ALL the time.
I pulled apart a few wiring connectors and all the contacts look clean on the idle air solenoid, TPS and maf sensor.
What could be wrong and how should I check it?
Dan S
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Dan, My '89 does the same thing, warm or cold. Idle is not adjustable and my mech isn't concerned about it. Still does the fluctuation when engaging the ac compressor with no sweat! Bob/Orlando
I have a 91 TBird with the 5.0L HO engine and AOD. It suddenly developed a high idle. I checked the linkage, nothing is binding or hanging up. I even unhooked all the cables from the throttle body, made sure it was closed and started it. High idle.
It idles about 2000 rpm. At first it would only idle high a few seconds when you first started it up. Now it idles high, ALL the time.
I pulled apart a few wiring connectors and all the contacts look clean on the idle air solenoid, TPS and maf sensor.
What could be wrong and how should I check it?
Dan S
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I have a 91 TBird with the 5.0L HO engine and AOD. It suddenly developed a high idle. I checked the linkage, nothing is binding or hanging up. I even unhooked all the cables from the throttle body, made sure it was closed and started it. High idle.
It idles about 2000 rpm. At first it would only idle high a few seconds when you first started it up. Now it idles high, ALL the time.
I pulled apart a few wiring connectors and all the contacts look clean on the idle air solenoid, TPS and maf sensor.
What could be wrong and how should I check it?
What happens when you pull the plug on the IAC motor/solenoid? Report back on this... also, it could be dirt or debris holding the throttle butterfly open a crack.
Rob * * *
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By IAC motor / solenoid, do you mean the air conditioning compressor? The air doesn't work so compressor isn't kicking in.
Let me know what this IAC looks like and I'll try unplugging it. Thanks. Dan

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"Dan" wrote

Nope. Idle Air Control valve. Diagonal thingy on the side of the throttle body.

http://www3.telus.net/neatcrap/iac.jpg
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Vacuum leak or bad Idle Speed Control Solenoid.
I have a 91 TBird with the 5.0L HO engine and AOD. It suddenly developed a high idle. I checked the linkage, nothing is binding or hanging up. I even unhooked all the cables from the throttle body, made sure it was closed and started it. High idle.
It idles about 2000 rpm. At first it would only idle high a few seconds when you first started it up. Now it idles high, ALL the time.
I pulled apart a few wiring connectors and all the contacts look clean on the idle air solenoid, TPS and maf sensor.
What could be wrong and how should I check it?
Dan S
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Sludged up idle air bypass; low engine coolant/air bubble/bad ECT or related wiring; maybe vacuum leak; IAC; to name a few items.
On Tue, 06 Jan 2004 14:08:28 -0700, Dan wrote:

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Have you checked the coolant temperature sensor and it's electrical contacts?
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No I haven't checked the sensor or it wires yet. I'll have to look around for it. This is a " new to me car".
I did what the other fellow asked and unplugged the IAC while it was running. It made zero, zip, nada, no difference. I kept plugging and unplugging it and it never did a thing for the idle.
Does this mean it is defective or just needs to be taken apart and cleaned?
It looks pretty easy to take off...
Dan

contacts?
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No I haven't checked the sensor or it wires yet. I'll have to look around for it. This is a " new to me car".
I did what the other fellow asked and unplugged the IAC while it was running. It made zero, zip, nada, no difference. I kept plugging and unplugging it and it never did a thing for the idle.
Does this mean it is defective or just needs to be taken apart and cleaned?
It looks pretty easy to take off...
===========================Nothing wrong with trying to clean it first. It is easy to take off, and is a very common problem on Fords of all ages.
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