I have an 89 f-250 4x4 with the 5.8l , the truck does well most of the time however when it is warming up but not at operating temp turning the turn signal on causes a drop out/bucking of the engine. When running the engine also randomly likes to stay at the speed it was previously at and will continue until slowed by braking or taking the clutch out , this will cause it to rev to about 2100 rpm and stay for 5 sec to 3 minutes

i have tried to remedy most of the common parts iac, tps,and map . the distributor and coil are new as well

 

i would check a couple of the basics before putting any more parts in ...
check the alternator output with a volt meter;
check that the throttle cable isn't frayed or hanging up for some reason.

 

both are good 14 volts and good throttle cable