91 Ford F150 big V8

[55 50 Ron]

It goes to 2000 to 2200 RPMs and won't slow down. IAC is new, If IAC is disconnected electrically, it slows down to 600 to 800 RPMs, but wants to stop, but picks up again and continues that hiccuping.

What needs to be checked next? Thanks

 

[Kitt]

Throttle position sensor?

 

[wore out]

It goes to 2000 to 2200 RPMs and won't slow down. IAC is new, If IAC is disconnected electrically, it slows down to 600 to 800 RPMs, but wants to stop, but picks up again and continues that hiccuping.

What needs to be checked next? Thanks

Is the CEL lit?

Have you scanned it for trouble codes?

 

[Ericp351]

Check for air leaks and do a vac. test. What is your engine? Little Windser? Thought no F 150 46O's.

 

[Ericp351]

Is the CEL lit?

Have you scanned it for trouble codes?

He ain't OBD II, so may have to use brains!.....

 

[55 50 Ron]

Throttle position sensor?

Where is that located on the engine? And thank you

 

[Carls70]

How long ago was the IAC valve replaced?
How did the symptoms come about?

If that one has the map sensor on the fire wall, check the rubber vacuum line running to it.
Some of the older Fords need to sit and run for 15~30 minutes to relearn the idle after disconnecting the battery/jump starting/replacing the IAC etc.

 

[Carls70]

Where is that located on the engine? And thank you

Should be under the intake below the throttle shaft/linkage (front of the engine right after the rubber air intake pipe enters the cast plenum)

I wouldn't recommend arbitrarily adjusting it.

 

[55 50 Ron]

Is the CEL lit?

Have you scanned it for trouble codes?

Don't know where the CEL is (I'm not "up to speed") on this truck !!!!

Have not scanned for codes.

 

[Carls70]

Don't know where the CEL is (I'm not "up to speed") on this truck !!!!

Have not scanned for codes.

Check Engine Light

 

[55 50 Ron]

Check for air leaks and do a vac. test. What is your engine? Little Windser? Thought no F 150 46O's.

5.8 liter EFI engine V8.

I don't know how to look for air leaks or do a vac test. Most likely I need to take the truck to a real mechanic.

 

[55 50 Ron]

How long ago was the IAC valve replaced?
How did the symptoms come about?

If that one has the map sensor on the fire wall, check the rubber vacuum line running to it.
Some of the older Fords need to sit and run for 15~30 minutes to relearn the idle after disconnecting the battery/jump starting/replacing the IAC etc.

The IAC is new.

What does the map sensor look like?

Thank for the note about "relearn the idle".

 

[Carls70]

The IAC is new.

What does the map sensor look like?

Thank for the note about "relearn the idle".

Rectangular black box about 2"x3"x1" with a mounting tab, single vacuum line and 3 wire connector. I've seen them mounted to the firewall and in fenderwells

 

[wore out]

The IAC is new.

What does the map sensor look like?

Thank for the note about "relearn the idle".

No sense taking it for a drive through the parts department without looking at possible trouble codes and viewing sensor outputs to see if all are in their expected range.

 

[Duner Wi]

It goes to 2000 to 2200 RPMs and won't slow down. IAC is new, If IAC is disconnected electrically, it slows down to 600 to 800 RPMs, but wants to stop, but picks up again and continues that hiccuping.

What needs to be checked next? Thanks

No Ford 1991expert but I believe there is an IAC relearn process .

 

[Ericp351]

First- not MAP- idel issue. Vac. leaks- examine hoses, then sprat WD 40 or like around suspect gaskets. Include upper + low intake, et cetera. Note- this rig does no "RE-Learn"! Come on guys, help this gentleman, ain't a 2001 Honda! EDIT- Fast check- examine hoses to PVC and Power Brake Booster- You sound lean- sucking air. Good Luck.

 

[used red MN]

Pull out the PCV valve and block all the other holes in the valve covers. See if it pulls a vacuum in the crankcase indicating a failed intake gasket on the lower side. Probably a more common problem on FE engines than M or Ws. Easy to check and eliminate.

 

[Stan Coryell]

It goes to 2000 to 2200 RPMs and won't slow down. IAC is new, If IAC is disconnected electrically, it slows down to 600 to 800 RPMs, but wants to stop, but picks up again and continues that hiccuping.

What needs to be checked next? Thanks

The trouble codes in OBD1 are limited, but I would still pull them. I have an old scanner with a Ford adapter, not that it helps you.

Check the TPS with the key on engine off at operating temperature. It should read less than one volt at idle and 5 volts at WOT.

I'd also check the base timing and for vacuum leaks.

 

[55 50 Ron]

Rectangular black box about 2"x3"x1" with a mounting tab, single vacuum line and 3 wire connector. I've seen them mounted to the firewall and in fenderwells

is this it see photo It's on a mechanical mount by the A/C. I pulled that line and the RPMs dropped to 1000. That line goes to the intake.

 

[used red MN]

The trouble codes in OBD1 are limited, but I would still pull them. I have an old scanner with a Ford adapter, not that it helps you.

Check the TPS with the key on engine off at operating temperature. It should read less than one volt at idle and 5 volts at WOT.

I'd also check the base timing and for vacuum leaks.

Here is a video showing how to check the codes by shorting the test plug terminals and reading the CEL flashes.
Ford OBD I codes