The most common symptoms of a bad exhaust gas recirculation valve are rough or misfiring idle, detonation, stalling and hard starting. The EGR valve is a component of an automobile’s exhaust circulation system that reduces pollution-causing emissions.
When an EGR valve functions incorrectly by leaking, becoming clogged or otherwise malfunctions, it results in poor engine performance. Because many EGR valves are mechanical, they are prone to becoming stuck in opened and closed positions. EGR valves that are stuck open cause poor idling, engine misfiring and stalling. If the valve is stuck closed, a nitrogen oxide builds up resulting in knocking and incorrect engine timing.
Mechanics can look for other causes by using a vacuum gauge to check for sufficient vacuum supply. No vacuum indicates a leak in the system. Mechanics can also examine the EGR valve stem to see if it moves while the engine is revving. If it does not move, the valve is bad and needs to be replaced. The valve also needs to be inspected for clogs and cleaned or replaced, if necessary.
Because EGR valve problems have a number of causes, the best way to diagnose the issue is to use a scanning tool that displays trouble codes. Vehicle service manuals list the proper repair protocol depending on the trouble codes.