Expert: Sean Halliday - 8/10/2010

Question
QUESTION: HI SEAN I HAVE A 1994 F150 WITH A 4.9. MY TRUCK HAS A ROUGH /SMOOTH IDLE AND WHEN I HIT THE GAS PEDAL IT STUMBLES AT FIRST .I HAVE CHANGED THE SPARK PLUGS,WIRES,DISTRIBUTER CAP, ROTOR,AND THE IGNITION CONTROL MODULE.COULD MY PROBLEM BE A VACUUM LEAK.

ANSWER: It could be the vacuum or a small leak at the intake.Test the vacuum with a vacuum leak tester and try cleaning the maf sensor.This is more fuel related so replace the fuel filter also.

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QUESTION: HI SEAN MY 94 F150 WANTS TO STALL WHEN I COME TO A STOP AND GO FROM FORWARD TO REVERSE.BEFORE IT STALLS THE IDLE GETS REALLY RUFF.

Answer
Usually this will be the idle air control solenoid or a dirty throttle bore.Can also be a vacuum leak but nearly always a bad iac.The check engine light will come on eventually to confirm this but try unplugging the iac and see what the idle does.If it varies then you found the fault.Spray around the intake also with brake cleaner to check for leaks.Possible egr valve sticking will cause this so its best to maybe have a shop look at it as there are several things that cause poor idle.