-Faulty O2 Sensor
-Faulty catalytic converter
-Faulty gas cap that is not tightened or is broken.
-Vacuum leaks
-Faulty ignition coil
-Faulty spark plug
-Faulty fuel injector
-Faulty head gasket
-Faulty EGR valve
-Faulty fuel pump
-Faulty MAP sensor
-Faulty camshaft or crankshaft sensor
-Faulty thermostat