High Idle - Need help

[Explorer1992_4.0]

Hi Guys,

New to this site

I have a 1992 Ford explorer XL..Currently have a high idle at 1300 - 1500 when warmed up ( Cold start is about 800 - 1000 )

IAC valve is disconnected..I plug the electrical connector to the IAC valve and the idle increases to 2000 RPM

I don't hear any vacuum leaks anywhere


Dan

 

[aldive]

Have you checked the thermostat?

 

[fixxxer]

Why is the IAC disconected? That is what controls the idle speed. Disconnect your battery, reconnect the IAC valve then reconnect the battery and start the truck. The computer will see the IAC back online and and adjust the stepper motor in it to regulate the idle properly. It may take 10-20 minutes (approx 10 mi) of driving for the computer to relearn it's idle settings with the IAC reconnected.

 

[Willard]

Since it's while warm, check the t-stat and temp sending unit (the one that goes to the engine computer) and see what that does. Otherwise you may have a faulty/dirty IAC. You could try cleaning that as well.

 

[Explorer1992_4.0]

Hi,


I bought the truck about 3 months ago...The IAC was disconnected then...I simply reconnected it and had an increase in idle speed

I also gave it a tune up ( Replaced all plugs,wires,filters ) did not change the thermostat though

 

[Explorer1992_4.0]

Hi,


Disconnected the battery and reconnected the IAC Valve...Idle is still at 1800 RPM after 15 - 20 min

 

[fixxxer]

At idle, the throttle plate should be almost completely closed,

that's when the IAC valve kicks in. It allows for a certain amount of metered air to bypass the throttle plate to give you the correct idle speed. If you have a stuck IAC valve or the throttle cable is hanging up or there is something in the throttle body keeping it from closing properly, your idle will be abnormally high

 

[Explorer1992_4.0]

Do i need to take it no a drive for a while or let it idle...

Is it possible to have a faulty IAC or a lower / upper intake manifold leak ?

Possible a sticky thermostat would cause this issue...Like i mentioned,i bought this vehile about 3 months ago as is

 

[Explorer1992_4.0]

Hi,


Drove the thing for 15 miles and no change in idle...No CEL on at all.

I'm beginning to think i should get a code reader to see if there is stored codes.

I'm also thinking it may have a lower intake manifold leak.

Thanks for all suggestions and help.

I'll post my repair a soon as i can

Dan

 

[mikeinri]

Welcome to the site!

I would start with cleaning or replacing the IAC. If that doesn't do it, check for stored codes. You might have a problem with the circuitry, I would expect that to give a code.

You might want to search for an electrical troubleshooting guide for this circuit. What you're looking for is something that tells you how much voltage (or resistance) you should see on each wire under certain conditions (using a voltmeter).

The engine temperature sensor is a common source of idling issues too, as mentioned.

But, since your issue seems to start with the IAC, I'd start there.

Hope this helps.

Mike