1993 F-150 5.0L 302 V-8 4x4 with Automatic trans.

My Truck runs okay at first but after driving and when it warms up, this problem occurs.
After I stop and shift from Drive to Park or Reverse, the idle fluctuates up & down between 450rpm and 1000. Sometimes after fluctuating for about 20sec it steadies out nice and smooth other times it continues until I hit the gas to rev it up. Occasionally it will stall out after shifting from Drive to Park and/or Rervse.

Do you know what may be causing the idle to perform this way and I what should check to correct the problem.

 

Mine was doing the same thing. I found out that it was the air conditioning compressor clutch cycling because it wa low on refrigerant, it's a thought anyway!

 

Test your TPS. I have the same truck you do, except mine is a 2wd and I would put it in gear and it would stall every time. I replaced it and tuned it and it hasn't given me a problem yet.




'93 F-150 loaded and modified!
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Sounds like the ISC motor on the side of the TB. Some try to clean them, but that don't fix them all the time. Cures 95% of all idle problems as long as you don't have any vacuum leaks or "check engine" light.

 

At the risk of exposing my ignorance, what does TPS stand for?
And while we're at it ISC, TB...?

Thanks

 

TPS= throttle position sensor
TB= throttle body
not sure about ISC motor

 

I think "ISC" is the IAC or Idle Air control, valve on the side of the throttle body.


'93 F-150 loaded and modified!
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You guys rule!!!!!!!!!!

The ISC is the IAC which is exactly the cure for the idle surging I've been dealing with for quite a while.

IAC did not show up on the Error Codes from the dealers mechanics.
They had a lot of ideas as to what it could have been, but you guys nailed it- thanks.

ps
the old one was stuck, so I ran 12 volts across it and it clicked and then shorted out- oh well.

 

When you replace it, do you replace the entire value or just the BPA-IAC?




'93 F-150 loaded and modified!
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>
>When you replace it, do you replace the entire value or just
>the BPA-IAC?
>
>
>
>
>'93 F-150 loaded and modified!
>Check my Gallery

Good question..
I have an intermittent surging problem with my '96 Windstar that the mechanic can't figure out.
It was suggested that the IAC was the culprit by an online service tech that has dealt with several 3.8 liter similarities.
The do-it-yourself guides at the auto parts store indicate that (at least for my vehicle) ya can't do it yourself because it has to be calibrated.....

I wish you the best (though I know this doesn't really help).

beaming1

 

I tried all of the "cheap" fixes, to no avail, on my '93 Aerostar before I repaced the valve(~$80)(I think Ford calls it the Idle Air Bypass Valve). In any case, it is what some call the IAC (Idle Air Control) valve. Once I replaced the valve my Aerostar ran smooth as silk. It is super simple to replace. As far as I know, there is no calibration required for this valve. The TPS(trottle position sensor), on the other hand would need calibration if replaced.