* Incorrect Air/Fuel Mixture: The IAC valve controls the amount of air entering the engine at idle. If it's malfunctioning, it might be letting in too much or too little air. This leads to an incorrect air/fuel mixture, making the engine run inefficiently and consume more fuel.
* Rough Idle: A bad IAC valve often results in a rough idle, where the engine stalls or hunts for the correct speed. This inconsistent operation wastes fuel.
* Increased Engine Load: To compensate for a lean or rich mixture caused by the faulty IAC valve, the engine might work harder, increasing its load and thus fuel consumption.
* Higher RPM at Idle: In some cases, a faulty IAC valve might cause the engine to idle at a higher RPM than normal, directly increasing fuel consumption.
So, while a bad IAC valve might manifest in other ways (rough idle, stalling), increased fuel consumption is a very likely symptom.
