Unnecessary High Idle

[mudbog42]

I posted a similar thread before but its doing it again now with a different carb. The idle gets stuck at about 1500 RPM's sometimes higher and I can't blip it down even after the whole truck has warmed up. Its real aggravating as I don't want to put in gear at that high of an idle. The only piece that swapped over from the carbs was the idle stop solenoid so I thought maybe that was it, replaced with a new one and about a week later the problem happens again. Any ideas?

 

[big dan]

have you checked under the hood to see if the throttle is shutting all the way? or if you can shut it by hand?
Ive had two similar problems, once it was the throttle shaft binding and I could only close it all the way by hand and the other time both throttle valves were closed and the idle was adjusted all the way down but there was something wrong with the carb and I ditched it.

on a side note a little funny story, I had a friend whose carb had a vaccum leak and he took it to a carb shop to get it tuned. instead of fixing the leak they turned the idle way up on the carb and every time he would put it in gear it would bark the tires.

 

[mudbog42]

I have checked and I can't move the throttle down anymore and I can't see any binding and this is the second carb that has done this and when it does finally drop it does'nt look like the throttle moved any further down or maybe its just my eyes?

 

[big dan]

well in that case I dont know what to tell you. sorry. like I said I had one do that where both throttle valves were completely closed and it was still turning about 1500-2000. I dont know what was wrong with it so I ended up getting a new one.

 

[diesel4me]

Q-jet?...

Only thing that can cause a fast idle is the idle speed screw adjusted in too far,or the secondary butterflies are not closing all the way,or the fast idle cam on the side of the carb is sticking on the fast idle portion of the cam..(often due to the choke not opening all the way)..and the idle stop solenoid being adjusted improperly,but you've already checked that possibility--vacuum leaks can cause fast idling too..