Very high Idle Problems

[1986gmc]

Ok so I have a 1986 gmc 1500 with a after market holley carb on in.I replaced my broken electric choke, changed the spark plugs,spark plug wires, and distributor rotor and cap. Now when I start the truck up it revs out at 4-5 thousand rpms. So now what I did right,spark plugs are all gapped right at.035,fireing order for wires is correct checked it several times, distributor should be fine I put it back on the same exact way it came off.I have the idle screw vertially all the way out think that would help it didnt, messed with themixture screws a little, but now have them set at default 3 turns out. I really dont know what could be causeing the problem, I was wondering if anyone had any ideas?

[66/87chevy]

WOW 4-5 grand !!!! I was going to say maybe check to see if a vacum line is not hooked up but it shouldn't make it rev that high. Sounds like maybe the throttle cable or linkage is sticking.

[Corts60]

The only way it could be revving that high is if the butterflies were open. Check and see what is binding up your throttle plates.

[Goldfinger]

adjust the high idle screw and check for vacuum leaks

[1986gmc]

I am pretty sure I got all the vaccum lines taken care of there was some that werent plugged, that was one of the other things I did. But i cant see to find a diagram of all the vaccum lines to correctly diagnose it. Also iIwas thinking that it could be a throttle problem, but I really dont know where to begin to trouble shoott that honetly.
CORTS60 Are you talking about the butterflies in the carb? Cause I'm thinking maybe that could be the problem thinking maybe the carb needs to be rebuilt, but I have no idea what the list number for the carb is its a holley and the closest I can come to the list number is 6404.

[Corts60]

You need to physically take off the air cleaner and look down at your butterflies. With the engine OFF, cycle or move your throttle linkage back and forth and ensure that the butterflies are closing properly.

[76stepsidechevy]

Originally Posted by Corts60

You need to physically take off the air cleaner and look down at your butterflies. With the engine OFF, cycle or move your throttle linkage back and forth and ensure that the butterflies are closing properly.

check to make sure the linkage doesn't hit the bottom of the air cleaner either.

[tucsonjwt]

x2 on the "butterfly", i.e. choke valve. Also, check the "fast idle" solenoid. It is supposed to kick out when the A/C is on so the engine does not stall out at idle from the extra drag of the A/C compressor and belt. I have the screw/stop turned all the way out, since my 454 pigs enough gas already and I don't want a high idle when stopped for a traffic light - I just let the engine idle real low with the A/C compressor on - or just turn off the A/C when stopped or set it on low.

[story]

I'm just wondering since you said you changed the Elec choke, if it was running fine before that??? If so I would check there before tearing all kinds of things apart.

[THE "10" SILVERADO]

Originally Posted by tucsonjwt

x2 on the "butterfly", i.e. choke valve. Also, check the "fast idle" solenoid. It is supposed to kick out when the A/C is on so the engine does not stall out at idle from the extra drag of the A/C compressor and belt. I have the screw/stop turned all the way out, since my 454 pigs enough gas already and I don't want a high idle when stopped for a traffic light - I just let the engine idle real low with the A/C compressor on - or just turn off the A/C when stopped or set it on low.

I plan on just turning the idle up on my SBC for the A/C. I didn't want to pay like 120$ for the dang thing.

[1986gmc]

My truck doesnt have a/c. But i did look in the carb and the butterflies look like they are open sightly, and when i move the throttle all the wall back it like clicks into a new position and then they are closed. Idk if that could be the problem? or how to adjust it to make them close, it doesnt seem like there is a way to adjust it. also the truck was running fine before i replaced the choke, just a little rough

[JCampbell]

Do you have cruise control? Check the linkage. Same thing happened to me when I rebuilt the TB on my Suburban. Turned out that the cruise linkage was bound up at the diaphragm thus holding the throttle open a bit.

[willett]

I used to have a holley carb. The rod that connected the throttle linkage to the butterfly goes through the carb casting. over time the hole that the rod ran through ovalized and caused my throttle not to return all the way..

It was kinda like cruise control though It never kept the revs anywhere above about 2200

I band-aid fixed it for a few weeks by running an extra return spring from the throttle linkage to the thermostat housing.

Its a long shot, but maybe this will help you.....

[1986gmc]

Ok so i dont have cruise control on the truck so that couldnt be the problem. i wish that would of been the problem. ok so willett you know i know exactly what you are talking about my carb is the same way.Ill go get a heavy duty spring, ill see how that works ill let you know, thanks alot for the idea.