TPS and ISC explanation in relation to the throttle plate and spring. FJ62 (1 Viewer)

[Saucerman]

So I ask this because in spite of changing the throttle cable the truck still has what I call an idle issue. Maybe I am mis-labeling that though. The truck will not return to normal idle after pushing through all 4 gears (converted to 4 spd) Most of the time I will have to tap the accelerator pedal to get the idle to come back down. The dash-pot has been removed. Even in gear I can feel it when the throttle is stuck open a bit, say in 4th and coasting in traffic. I can tap the accelerator and can feel the idle come down. The TPS has been replaced and set to spec. I was just wondering it that little piece can actually keep the throttle from closing all the way. Or even if closed all the way would that little spinning part of the TPS keep the idle unnecessarily high? The ISC I could only clean as I could not find a replacement. Outside of that it runs pretty well. It just sucks to pull up at a stop sign and the motor is reveing to 1800 rpm.

 

[Lead Head]

Why did you create another thread? As others mentioned in your other thread, you need to verify whether or not forcing the throttle valve back to idle by hand (as in grab the throttle linkage and twist it back) brings it back down to idle. If it does, your issue is the throttle valve binding in the throttle body.

...and why did you remove the dashpot? It serves a purpose.

 

[Saucerman]

Well, started another thread because this was another question. my dashpot was broken so it served no purpose whatsoever. So, of course if grabbing the throttle by had worked I would not have posted this. I guess at a traffic light I could jump out and try but gee, never seems to safe. Haven't been able to duplicate the problem in the saftey of the neighborhood, but thanks for you input.

 

[Lead Head]

You need to figure out how to reproduce the issue reliably. i.e. does slowly letting off the throttle cause the idle to hang. Does it only happen while moving, etc...

 

[Godwin]

I've been dealing with this same issue for years, but my high idle is about 1,000 or so. Tapping the accelarator pedal will bring down a few hundred rpm to what should be normal. If I sort out the issue I'll post up.

Also dash pot has been removed, TPS reset, throttle plate and bore cleaned, cable externally is not hanging on anything, IOW nothing obvious is causing the idle to stick.

 

[Spook50]

It sounds to me like either the shaft in the throttle body is binding, or the return spring is getting worn enough to not be as strong as it once was. Possibly a combination of both even. I can't remember from the last time I had my throttle body off if it looked easy to remove the shaft and inspect/lubricate the bushings, but I can't imagine it would be too difficult as long as you can remove the plate without stripping the screw heads (I've done this on two throttle bodies).

I can't remember if you said you've already replaced the throttle cable or not (or at least lubed it), but if not that could also be something to check.

How about the pivot joint and return spring for the pedal itself?

 

[Saucerman]

It sounds to me like either the shaft in the throttle body is binding, or the return spring is getting worn enough to not be as strong as it once was. Possibly a combination of both even. I can't remember from the last time I had my throttle body off if it looked easy to remove the shaft and inspect/lubricate the bushings, but I can't imagine it would be too difficult as long as you can remove the plate without stripping the screw heads (I've done this on two throttle bodies).

I can't remember if you said you've already replaced the throttle cable or not (or at least lubed it), but if not that could also be something to check.

How about the pivot joint and return spring for the pedal itself?

Hey @Godwin , @Spook50 indeed cable replaced. spring on the pedal is okay and not binding. Took it off when replacing the cable. It occurred to me today that the old kickdown cable used to provide some extra tension. I added an extra spring so the soft peach of a gas pedal is now gone but so far today the truck came back down to near regular idle every time I stopped. I think Spook may be right, in that if it keeps up the throttle plate may need to be removed. I cleaned the TB well, but never lubed the bushings. Those are tiny flathead screws if I remember correctly. That might just do the trick and then I can lose that extra spring. I was just unsure if the TPS by itself could actually hold the throttle open, if that was possible at all. Thanks fellows.

 

[tornadoalleycruiser]

Food for thought. I am running a 3fe and h55 and will be adding an extra spring to the throttle plate. It hangs a little causing a high idle. From what I can tell the auto cable added that little spring to its step. I can blip it or push it by hand and it will drop back to normal idle.

 

[Godwin]

Food for thought. I am running a 3fe and h55 and will be adding an extra spring to the throttle plate. It hangs a little causing a high idle. From what I can tell the auto cable added that little spring to its step. I can blip it or push it by hand and it will drop back to normal idle.

The loss of the auto cable may be the answer. When I swapped the 3FE into the FJ60 I deleted the A440F and used a H42 so have never driven this particular 3FE with an auto tranny.