no idle speed adjustment?

[koda2000]

i don't believe there's supposed to be a way to manually up the idle speed as it's controlled by the PCM, but there's a screw on the T/B that can adjust the throttle plate. if you turn this screw in it opens the T/B plate, which effectively increases engine speed. as there's no difference between someone slightly pressing the gas pedal or turning this screw in, how is it there's no idle speed adjustment?

BTW: turning this screw OUT can cause the T/B plate to stick closed (ask me how i know).

 

[deweyville65]

i don't believe there's supposed to be a way to manually up the idle speed as it's controlled by the PCM, but there's a screw on the T/B that can adjust the throttle plate. if you turn this screw in it opens the T/B plate, which effectively increases engine speed. as there's no difference between someone slightly pressing the gas pedal or turning this screw in, how is it there's no idle speed adjustment?

BTW: turning this screw OUT can cause the T/B plate to stick closed (ask me how i know).

Morning Koda. Been there done that. I think it all boils down to "legalese"to keep Ford from being sued by the government. Just my thought. But I have argued before, that you definitely can raise the idle speed. Had to do that when the IAC valve went on vacation last year.

 

[jremington59]

The manual says there's no way to adjust idle, but I used the "throttle screw" to raise my idle with a bad IAC also.

 

[imp]

Throttle Plate Binding

Design of the throttle plate is exactly the same as in a carburetor bore, only bigger, which makes the possibility of "binding" in the closed position by scraping the edge of the plate in the bore. Worse yet, would be "overcentering" it in the opposite direction. Assembly line set-ups being what they are, added to manufacturing tolerances, prevent keeping the plate and bore diameters within tight enough specs to prevent problems. The fix was to place an adjustment screw to "stop" plate closure, while allowing initial idle air flow (not engine speed) to be near-zero. imp

 

[Turdle]

You can "adjust" the idle speed, but what have you done to the Throttle position sensor output at idle?

TPS voltage must be less than 1v at idle or problems will occur.

 

[koda2000]

You can "adjust" the idle speed, but what have you done to the Throttle position sensor output at idle?

TPS voltage must be less than 1v at idle or problems will occur.

yes, i get that. that's why i said "turning the screw or slightly stepping on the gas pedal have the same effect". either way effects the TPS and thus the idle speed. right?

 

[DjDom]

Hmm, this could be a fix to my rough idle if you can find how to do it.
Since mine idles rough at about 750-800 but is smooth from 900-1000, I can just up the idle a bit.

 

[bill06447]

Low idle is a symptom of a problem, don't just cover it up, fix the problem!! Clean the IAC to start.

Bill

 

[1992fordgreen]

The TPS is best when it reads Open circuit on the terminals. Like Turdle said, below 1v should be good.

 

[2000StreetRod]

PCM commands the idle speed

The crankshaft position sensor allows the PCM to determine the engine speed. The TPS allows the PCM to determine when the engine is at idle. The DTR sensor allows the PCM to determine what transmission position is selected. On the second generation Explorers the PCM commands the IAC valve to a predetermined idle speed. Park and Neutral have a different commanded idle speed than other in gear selections to reduce creep and transmission overheating. The PCM computes a delta for the IAC valve by comparing the actual engine speed to the commanded idle speed and applies the delta to achieve the desired rpm. The PCM reads the TPS at engine start and assumes the voltage to be closed throttle and stores the value. The PCM periodically reads the TPS voltage and when one that is lower than the stored is read the PCM makes that the new closed throttle value. I don't remember what year of production eliminated the need to get the closed throttle voltage to around 1.0 volts.

I adjusted my throttle plate stop screw (when the engine was idling normally with no problems) to barely run when the IAC valve connector was disconnected. That way I would know I had an IAC valve issue if the idle speed dropped below normal but the engine wouldn't die on the way home to fix the IAC valve. See Idle adjustment procedure