WHAT CAN CAUSE ENGINE TO RACE AFTER WARMED UP?...

1988 Ford F-150

Tiny

ford9fan

December, 2, 2012 AT 6:13 PM

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.

9 Answers

Tiny

ASEMaster6371

December, 2, 2012 AT 6:52 PM

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

Tiny

ford9fan

December, 2, 2012 AT 7:49 PM

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

Tiny

homer1967

December, 2, 2012 AT 8:29 PM

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)

Tiny

ASEMaster6371

December, 2, 2012 AT 8:33 PM

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

Tiny

ford9fan

December, 2, 2012 AT 9:01 PM

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

December, 2, 2012 AT 9:02 PM

Engine was warm.

Tiny

homer1967

December, 2, 2012 AT 9:21 PM

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.

Tiny

ford9fan

December, 3, 2012 AT 1:16 AM

Thanks for the try.

Craig

Tiny

homer1967

December, 3, 2012 AT 2:51 AM

You are welcome. Thank you for coosing 2carpros

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