Mechanics

FORD F-150 ENGINE PROBLEM

1988 Ford F-150 • 140,000 miles

What can cause engine to race after warmed up?
When first started it idles as it should, then slows as it warms, then after it is fully warmed the engine idle starts to increase until it reaches about 3000 rpm's without touching the throttle.
It has been checked for vacuum leaks and the Idle Air Control Valve was first cleaned then replaced, with no change.
It also has a new fuel pump and pressure regulator.
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Ford9fan
December 2, 2012.



I would look for vacuum leaks. Common issue.

Did anyone check the control for the idle air control? If you disconnect it, does the idle return to normal?

Roy

The engine has no vacuum leaks.
The engine shuts off when the idle air control is disconnected.

Tiny
Ford9fan
Dec 2, 2012.
How did you check for vacum leaks?Was the engine hot or cold? What size motor? If you are sure that there is no vacum leaks then I wouls suspect the tps sensor.(Throttle position sensor)

Homer1967
Dec 2, 2012.
Ok, good, then the situation is around the idle control motor.

The motor should idle at 500 rpm with it disconnected.

You need to see if it is being commanded on when the idle rises or the valve is bad.

I still need the motor size

Roy

5.0
Checked hoses visually, starting fluid around gaskets and areas not easy to check.
Idle control was replaced after cleaning original failed to correct the problem.

Tiny
Ford9fan
Dec 2, 2012.
Engine was warm.

Tiny
Ford9fan
Dec 2, 2012.
I am going to have to suggest that you take it to a shop at this point, because to diagnose any further is going to take specific tooling and the ability to know what the information you gather means. You have covered thae basics and it is just cost to much to keep throwing parts at it. Thanks.

Homer1967
Dec 2, 2012.
Thanks for the try.

Craig
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Tiny
Ford9fan
Dec 3, 2012.
You are welcome. Thank you for coosing 2carpros

Homer1967
Dec 3, 2012.

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