Q: My XC90 Volvo 2006 I thought was the PCV system so I had all the hoses there changed as well as the oil catch can but my engine li

There are more than ten principal causes of rough idle and that list doesn’t include potential mechanical faults such as uneven cylinder compression. By far, the most efficient strategy to resolve this issue is to request a rough engine idle diagnostic. The responding certified mechanic can scope the cylinder firing patterns, in each cylinder, and see, at a glance, if the problem stems from a few faulty cylinders or if there is a global engine management problem. Among the more notable causes of rough engine idle are a stuck open EGR (exhaust gas recirculation) valve, dirty fuel injectors, incorrect idle speed setting, vacuum leaks, incorrectly installed or damaged spark plugs, defective or clogged fuel pump, clogged fuel filter, failing electronic components such as the ignition control module, plug wires, coils, and spark plugs, a defective airflow sensor, and dirty oxygen sensors.