2.8 high idle until i tap the gas

bigmelton · May 31, 2013

Every time I start it or when i come to a stop it has a high idle until I tap the gas real quick, then it idles down. It is a 84 bronco 2 with a 5 speed. Any ideals on what it could be?

RonD · May 31, 2013

High idle on a cold engine is normal.

You should have a motorcraft 2150 carburetor, it will have a choke plate at the top of the carb that closes when engine(choke spring) is cold, this can also have a cam that holds the throttle plate(bottom of the carb) open a little more at idle until engine(choke spring) warms up.
If the choke spring is broken or out of adjustment this cam can become loose and moves while driving so when you come to idle again it idles high, a tap on the pedal releases the cam so idle goes to normal.

A loose throttle plate can act the same way, doesn't close all the way, unless tapped.

Because tapping the gas pedal works to reduce the idle it sounds like a mechanical issue.

Google: Motorcraft 2150 2V Carburetor theory

Nice page with pictures and suggestion on how this carb works

Surrey · May 31, 2013

Carbureted engines are designed to idle high when cold. That part is normal. (and yes, hitting the gas to drop the rpm is normal behavior)

Does it idle high when you stop even when the vehicle is warmed up? If it does, then you have a problem... As Ron said, its probably mechanical, and probably related to the choke on your carb. If these symptoms only exist while its cold, then everything is probably working fine.

bigmelton · May 31, 2013

I understand that it should idle high when cold but it does this all the time even after it is warmed up. the electric choke has been rigged to keep the choke plate wide open and doesnt move. I'm thinking it may be a loose throttle plate.

PetesPonies · May 31, 2013

With the choke plate "rigged" open, you still have the fast idle cam resting againt the idle screw, thus fast idle. It's why you shjouldn't "rig" things unless you understand exactly what you are doing :icon_surprised:

dangerranger83 · May 31, 2013

Mine did the samething, I just got use to tapping the gas pedal and before I knew it, it became a habit I didn't really notice I was doing.

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Lil-Pony · May 31, 2013

mine did this even when my engine was warmed up along time ago, my mechanic disconnected something and now it idles high on start till i tap the gas and it never idles high again until it cools down on the next start up.

wildbill23c · May 31, 2013

bigmelton said:
I understand that it should idle high when cold but it does this all the time even after it is warmed up. the electric choke has been rigged to keep the choke plate wide open and doesnt move. I'm thinking it may be a loose throttle plate.

Double check how that choke plate is being held open, if its held open improperly it can cause the fast idle cam to be stuck causing it to be stuck in high idle. If that choke isn't working properly, its best to just disconnect it completely rather than try to hold the choke plate open. Mine was rigged like that when I first got it, I just disconnected the choke completely and have a piece of wire holding just the plate in the open position. I got through the winter even in sub zero temps without a choke so it must not be to important LOL.

Renny · Jun 4, 2013

Mine also does this and on mine I think its the throttle positioner sliding back slowly. Mine is electrically operated and I'm not sure what generates the signal. I haven't tried disconnecting and instead have just gotten used to blipping the throttle like everyone else.

bigmelton · Jul 1, 2013

My choke is electric and on the inside is a metal coil. When it would heat up the coil would unwind and start opening the choke plate. It was unplugged when i got the b2 but i wired it up and it would work but i still had the same idle problems. So I just unhooked it and then rotated it so it would hold the choke plate open all the time. I really dont need a choke cause it never has a problem starting in cold weather. Maybe I need to look into the fast idle cam?

PetesPonies · Jul 1, 2013

Yes its possible the choke plate is opening but you are never able to clear the fast idle cam to lower the idle.

70roadrunner · Jul 1, 2013

I think they all do that! mine did the same thing. I just got used to it. clean the linkages on the carb, then spray it generously with silicone spray lubricant

2.8 high idle until i tap the gas

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