1987 D150 idles super high in park or neutral, mostly after the engine warms up. It drives just fine, but put it in park and it sounds like it’s around 3000 RPM.

The engine will diesel for a while after I shut it off. Not sure if that’s related or a separate problem. It’s in need of a good tune up which my fix the diesel, but I’ve never been able to straighten out the high idle.

Thanks!

 

have you checked the choke to make sure it is open? is the throttle returning to the closed position and if so do you have the curb idle set screw adjusted correctly?

 

The choke is nearly fully open all of the time. It never closes, even by hand. Not sure if it should do that! I’m brand new to the world of carburetors, so it’s time to learn.

I can operate the throttle by hand and it does return to the closed position.

I’m not sure about the curb idle screw. I managed to find it today and adjust it by hand just to verify what it was. I have a tachometer coming today so I can get it properly adjusted. What is the procedure for getting it set just right?

Side note, I was driving it around yesterday and noticed (sometimes) it will shift really hard into drive and reverse, you can feel the vehicle shake with how hard it shifts. When I let off the brake the truck rockets forward as if I were giving it gas when I’m not.

 

if it is idling too high still that may be causing your issues. if the choke is not closing when cold that is likely an issue. with the choke open i would try turning the curb idle screw out to bring the idle down to what is reasonable. you don't necessarily need a tach to set idle speed. bring it down till you experience stalling when you put it in gear and then bring it up a tiny bit to prevent stalling. what type of carb is it? if you can include pictures it would maybe help definitely need a working choke if you want it to start easily but if you live someone warm all year round it may not be too bad without a working choke.

 

Fairly certain it’s a Holley 6280. It’s marked R40222 in a ‘87 D150 318.

I jiggled the choke plate a bit and got it to close as far as seen in the photo.

 

don't try to force the choke closed. you usually need to open the throttle to close the choke. as far as carbs go you have the lean burn system so i really don't have a ton of knowledge on them. i do see the throttle is not touching the sensor so i would assume that it may be part of the issue unless the choke is causing this. may have to hold the choke open while opening the throttle to see if you can get it to return the the sensor. if that doesn't work i would keep turning the throttle stop screw out till they touch.

 

I’m assuming you’re referring to what’s in this photo. I was operating the throttle by hand with the truck off. I let go of the throttle and it released, “slammed” forward, and the throttle is now touching that plunger looking device on the solenoid (name?).

 

ok as long as the throttle is returning to it. i believe it is a sensor so the computer knows when the throttle is closed but like i said i am not super familiar with this system. most people toss the system in the garbage unless they live in California.

 

This is a California truck I picked up before I moved to Washington. It idles amazing now. I wonder if something was just gummed up and stuck.

 

maybe. if you give it gas does it return like it should? i would almost wonder if you may have been having issues with choke linkage. the choke will usually hold the throttle open some till the choke fully opens and you give it gas and it starts using the idle stop.