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having problem with bucking and surging on 1991 Ford Ranger

bucking surges at a stop. i have replaced mas and computer and truck still bucking and surges. no codes.

Asked by for the 1991 Ford Ranger
It could be many things, unfortunately and without experiencing the problem first hand or being able to do some basic diagnostic tests its hard to say. Look for air/vacuum leaks around the intake manifold. Look to see if the EGR valve either leaks or does not seal/fully close. Important to look and see the ignition system isn't causing the misfire/stumble.
if ignition is causeing mis fire would it show a code