I have a '86 F-150 straight 6 carb. motor. My problem is the engine keeps

hesitating. I've changed plugs, wires, cap, rotor, fuel filter, all my fluids are

topped off, I sprayed the carb. with cleaner, change air filter and put

Sea-foam down it. It drives on the highway fine but if I stop, the engine idol

slows down and kills itself time to time. Does anybody have an Idea what I

can check? Thx.

 

Check for a vacuum leak.

 

Thats my guess, Especially if it Just started happening.
Also you might check Ignition timing.
To check for vacuum leaks, Use a can of carb cleaner and lightly mist all the visible vacuum lines and fittings(staying clear of exhaust manifolds of course) and see if the idle speed changes when you spray a fitting. If it does, then there's your leak!
A safer alternative is to use a mechanics stethescope with the steel rod removed , Just use the rubber tube, You can hear alot of stuff with the scope!

 

Figured it out this weekend and had a guy put a vacuum gauge on it and it

boiled down to the EGR valve wasn't opening. Replaced it and it started

running normal again. Thx for your help and insight.