86 gmc k1500 5.7L just replaced carb and now cant get engine to idle

Check for vacuum leaks

You seldom touch any carb adjustments,
there good for years,sometimes decades

I have a 30 year vehicle & only check them every
2 years at inspection time.

Only idles high because you have unmetered air
or vacuum leak or timing is off

If the problem is not a vac leak, it could be the idle circuit inside the carb. You may have to replace or rebuild the carb to fix it.

If the check engine light is on, you would need to check the computer for trouble codes first.
If the engine is fuel injected, it could be a bad injector. If it has a carb, it could be a sticking choke or an internal leak.

Your carb has an electric metering rod and a throttle position sensor.
The metering rod may be faulty, or there may be dirt in the passages for the idle circuit.
Can you keep the engine running with some pressure on the gas pedal ?
If there are no vac leaks, you may have to get the carb fixed. A replacement is several hundred dollars.

I don't have a diagram but I think the replacement carburetor may have come off an engine that had a governor which was activated by a plunger under the distributor plate. The vacuum lines went between the carburetor and distributor. Check to see if there is vacuum at one of the lines when the engine is runnuing. If there is just plug it off. A vacuum leak could be causing your idle problem.

Could they possibly have gotten the timing(check it with a light) off or distributor turned wrong? don-ohio

internal vacuum leak in carb. replace with weber carb you will be very happy

This is only a suggestion because it worked for me. With a cool engine, use a can of store brand carb cleaner and spray the heck out of it. Get it into the linkage well and let it sit for up to and hour or so....stuff some rags on the intake manifold to soak up the excess. Then, after letting it sit, get your 'Burb up to operating temp. Should be the ticket for you....and no, your engine won't catch fire.

Im not sure if this can help, but my 2000 gmc sierra was idling badly. Replaced Fuel Pressure Regulator and my truck runs like its brand new. My service engine light was also on.

The later 80's accords have a problem with idling being to high at start up, even when the ambient air temp does not warrant it. I have had a 86 and now an 87 accord and both did that. I pretty much deal with it, being as you cant hardly replace indiv carb parts. Adjusting the idle will do nothing to stop it either. I took my 86 to a shop when I still had it and he fixed it, but I cant remember what all he did. I know he drilled a couple small holes in the choke plate. I think that the thermowax valve is bad, but again, you cannot find just a thermowax valve or anybody who knows what it is. Replacement carb in my area is about $450. Like I said, you might just have to learn to live with a high idle at start up.