350 idle drops after hard drive

[Jakethesnake73]

After i drive down the highway against the wind the truck drops in idle when i stop.  Also i have my idle at 800ish when i hit the gas really quick from a stop and let off it wants to die or does die. I have a new fuel pump and filter. Could this be a carb issue? Im thinking its more related to plugging of the in tank screen.  It runss great oherwise

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[zieg85]

I would look at your linkage, it sounds like it may be hanging up and not fully dropping off the high idle cam.  At least that is where I would start.

[Irish_Alley]

transmission?

is the 800 rpms set at cold?

year, make and model?

[bd]

Other possibilities are weak idle solenoid, worn throttle shaft bore, poor state of engine tune....

[travisr1988]

I have the opposite issue most of the time. Sometimes the idle will drop, but it usually just keeps building up as I drive, it'll start at 750 warm, then after 10 minutes of traffic it will be at 800, then 900, then 950, then I have to shut it off in gear or it will diesel, and even then sometimes it picks up enough to diesel in gear although that's rare. The timing is at 2° advance, new distributer, old quadrajet. The carb is likely the issue in my case as I can adjust the idle mix screws with no change until either the throttle opens and closes or I shut it down and restart it.

[Irish_Alley]

I have the opposite issue most of the time. Sometimes the idle will drop, but it usually just keeps building up as I drive, it'll start at 750 warm, then after 10 minutes of traffic it will be at 800, then 900, then 950, then I have to shut it off in gear or it will diesel, and even then sometimes it picks up enough to diesel in gear although that's rare. The timing is at 2° advance, new distributer, old quadrajet. The carb is likely the issue in my case as I can adjust the idle mix screws with no change until either the throttle opens and closes or I shut it down and restart it.

i would be looking at a vacuum leak. prob the base plate at the carb or even the throttle bushings

[travisr1988]

Irish, I just put a new carb on this weekend and it seemed to have solved that issue as well as many others. It picks up a little idle speed still, but not near as much.

[Irish_Alley]

if youre sure theres no vacuum leaks i would set timing and make sure your vacuum advance is hooked up to manifold vacuum and working