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RE: Ask the Car Guy @socky July 7
A bad idle air control valve can cause the vehicle to idle badly. You can also find that when the AC is in use, the engine could die or idle really bad.
The mass air flow can cause many issues. Bad idle, engine stall, jerking, difficulty to start, or poor performance.
Well it's sometimes racing and then suddenly drops to running rough and low rpms when near idle. Sometimes it's kicking when accelerating. I'm thinking it's the airflow sensor.
It's a 2001 Ford Taurus.
You may want to check for vacuum leaks. A leak will bypass the mass air flow sensor and cause a lean condition. The mass air flow sensor operates by passing current through thin wires. The wires are cooled by the air traveling through the intake and this can be measured. If the mass air flow sensor is dirty, the computer will think that there is a small amount of air entering the engine and will create a lean condition.
Does it only happen when the AC is running?
This has happened before on other Ford Taurus. It could be a bad alternator or something that is pulling a large load on the electrical system. It sounds crazy, but here is the reason. Ford programmed the ecm to raise the engine rpm to raise alternator output rather than cut off the a/c. At low RPM, the alternator puts out low voltage. If the alternator is under performing or there are extra loads on the electrical system like an aftermarket sound system, then this could be your problem.
What car is it and what year?