Mechanics

CAR RUNS BUT SOMETIMES MAKES A HUMMING NOISE AND SHUT OFF THE CAR EXCEPT WHEN I PRESS GAS PEDAL IT WILL STAY ON

1991 Lincoln Town Car

Car runs but sometimes when I'm not pressing gas pedal it will make a loud humming sound then car will shut off unless I press the gas pedal
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Rj198012
November 17, 2011.




This sounds like the Idle Air Control Valve has failed. It controls idle and keeps the car from stalling when load is put on the engine. This is from, accessories being on, decelration or quick changes in decreasing speed, changes in the pedal position and when coming to a stop. It does so by opening ports and this changes the mixture in an attempt to keep the idle steady.
This is related to another issue that could be the problem. A vacuum leak could be causing the howling noise as the leak is sucking air into a crack in a vacuum hose. The IACV is fed by a vacuum hose and is often a lrge one. It will demand more vacuum wioth the changes that I mentioned earlier. This in turn will make the noise and casue the stall or idle problem.
So, first look for a vacuum leak and then check the IACV.



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