Q&A

 Master

A rough running 4 cylinder engine say a 4 cylinder engine running on 3 cylinders will run 25% rougher than an engine running on all cylinders. A rough running engine can seem like a bad engine mount. An EGR valve recirculates exhaust gas into the intake manifold under certain criteria. If this exhaust gas is allowed into the intake manifold at idle due to a defective EGR valve it will effect the engine idle condition. Your car has On Board Diagnostic capabilities if a Check Engine/Service Engine soon light comes on a code will be stored in the powertrain computer in your car that is retrieved by using a scan tool connected to (a common to all 1996 onward) a 16 pin diagnostic socket under the dash of the car. The code stored will indicate if there is problem with the fuel mixture, EGR system, ignition system ,misfire, fuel trim ect.......
A vacuum leak can cause an engine to run rough. As the engine warms up sometimes metal expands and a vacuum leak can seal up or at least be reduced but either way it will probably show up in fuel trim figures, O2 Sensor readings on the scan tool.