Surging idle in cooler temps

[84K30]

Over the past month, my K30 has become ornery when the temperature is under 50. It fires right up but the high idle from being choked doesn't seem to shut off for quite some time. This can be remedied by "stabbing" the throttle which brings the idle down to a normal speed. If I do not do this, the engine diesels when I turn it off. Engine is a 454. Carb has been replaced with a 600 com Edelbrock 1406 4bbl carb with an electric choke. I hit the linkage with some WD 40 today but I haven't noted any change. Planning on doing a full ignition tune up including rotor, cap, coil, wires and plugs. I then intend to set both idle speeds. Probably do 1200 for the high and 700 for the normal. After that, I will adjust the fuel mixture screws with a vacuum gauge. What else should I look for or try to address this issue? How about a new throttle cable?


Thanks,
Eric

 

[84K30]

Update: this issue seems to be entirely mechanical. The throttle cable is not resetting unless I manually do it by hitting the pedal or, if the hood is open and the truck is stationary, reset it manually by pushing the linkage forward. Could it be as simple as replacing the throttle return spring? Or is it more likely something more complex like a throttle shaft bushing? I was told the carb was “just rebuilt” by the previous owner. If it turns out to be something more involved, I may consider replacing the carb with a new 750cfm one. If a video would help, please let me know and I’ll do my best to upload one.

Thanks,
Eric

 

[Joshua Keith]

Update: this issue seems to be entirely mechanical. The throttle cable is not resetting unless I manually do it by hitting the pedal or, if the hood is open and the truck is stationary, reset it manually by pushing the linkage forward. Could it be as simple as replacing the throttle return spring? Or is it more likely something more complex like a throttle shaft bushing? I was told the carb was “just rebuilt” by the previous owner. If it turns out to be something more involved, I may consider replacing the carb with a new 750cfm one. If a video would help, please let me know and I’ll do my best to upload one.

Thanks,
Eric

I honestly didn’t know that the idle goes back down as the choke opens. I thought you had to hit the gas pedal for it to idle down.

 

[TubeTruck]

I've never owned a vehicle where I didn't have to stab the throttle to get it to kick down

 

[Conejo_K10]

Sounds like there may be some stiction in the choke linkage. Unless you drive really slow, the choke should disengage when the throttle is opened past 20-30%.
On my Q-Jet the choke is spring loaded and as I open the throttle it releases. I almost prefer a manual choke with intermittent reliability of the auto chokes.

How many return springs do you have. You should have at a minimum 2. Perhaps the spring rate is too low?
Tip: If you have both springs on the same side the shaft bushing will wear faster. I have mine on opposite sides to even the load.