Engine idle out of whack? Tell you what-if your car runs with electronic fuel injection, then it has to have an electronic control unit (ECU). Have a mechanic connect a scan tool onto the onboard diagnosticsport under your car's dashboard to pull whatever fault codes have been registered into your ECU's memory banks. Chances are, you'll get an idle control valve error, which means that particular valve has kicked the bucket. Now, you're probably wondering what the idle control valve is. Simply put, it's the valve that controls the flow of air into your engine when it's idling. The ECU measures the amount of air needed by the engine, and sends commands to the idle valve. When your foot's off the gas pedal, the throttle is closed. The idle valve opens and closes the bypass channel in your throttle to let that little bit of air in for idling. Now, if the idle valve conks out, it can freeze in either open or close position, screwing up your engine's idle speed. Get the picture? In short, once your idle control valve fails, your engine will either choke on either too little or too much air. Its idle speed isn't kept under control. Fortunately, replacement valves are available here at Car Stuff.