1989 Ford F150 engine stalls when returning to idle

1989 FORD F-150
71,900 MILES • V8 • 4WD • MANUAL
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WARD1955
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I have had problems with the engine stalling when I push in the clutch to change to a lower gear or when I am coming to a stop and push in the clutch. At times, the engine will lope from high to low rpm, high to lower, high to lower until it stalls...other times it does fine. After a stall, it starts right up with the turn of the key. Another symptom...the check engine light will flash on and off at times as I'm driving down the road.
A local Ford dealer could not help...per their suggestions/work...the back of the throttle plates were cleaned, the O2 sensor was replaced, the air by pass valve was sticking and cleaned with Wynns fuel injection service, the fuel filter was replaced, the fuel injection system was flushed, the back of the throttle plates were cleaned again, the crankcase breather was replaced and the filter assembly "FOFG" ??? was replaced, the "valve asy-thro" was replaced......I have made several trip to the local dealer with no success I have reciepts from the year 2000 when the problem began and gave up for a few years to drive a Honda Accord which I just turned over to my daughter...I'll miss that little car....please help as I have to drive the truck again, Thank you
Dec 20, 2007 at 8:48 AM
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BLACKOP555
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first have your truck scanned for trouble codes.

then post them back here, if there is none i think you should clean or replace your IAC module. also clean the egr valve and its passages and turn up the idle a bit.
Dec 28, 2007 at 10:10 AM
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WARD1955
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[quote:e72f48fb41="blackop555"]first have your truck scanned for trouble codes.

then post them back here, if there is none i think you should clean or replace your IAC module. also clean the egr valve and its passages and turn up the idle a bit.[/quote:e72f48fb41]

Since first sending you a message, I have replaced the O2 sensor and had a code 23 show up (TP sensor out of self test range)...I removed the TP sensor and tested the resistance cold and hot and it seems to be working .001m ohms to .009m ohms respectively...I tested the MAP and got a reading (left to right facing the motor) 0 volts to ground on the first wire, 0 volts to ground on the second wire, and 2.75 volts to ground on the third wire. I had already removed and cleaned the EGR valve and passage way (with a small wire cable). I continued to have stalling problems but no more infrequent flashing engine light.
Upon recieving your e-mail, I removed and cleaned the air throttle body and the air bypass valve. I cleaned the EFI upper intake area closest to where the air throttle body mounts. I removed and tested the throttle position sensor and found variable resistances at varied settings (seems to be working). I think the cleaning may have solved the problem but am skeptical as I have rejoiced prematurely on several other occasions... thank you for you response and I'll
Dec 31, 2007 at 8:15 AM
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BLACKOP555
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for the tp sensor, it has to be alligned perfectly when put in if its not perfectly realigned then it wont function properly!
Dec 31, 2007 at 9:54 AM
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INDYUKE
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blackop is right. The TP sensor needs to be aligned so that it reads 0.96 volts at the throttle's idle position. Between 0.94v and 0.98v is acceptable, but i have seen anywhere between 0.80v and 1.05v on some vehicles. The trucks that have electronically controlled transmissions which take their shift points off the throttle position experience major shifting problems with the TP sensor not set correctly.
Jan 1, 2008 at 12:58 AM
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