The Check Engine Light can illuminate with codes due to the lack of EGR (exhaust gas recirculation) flow caused by the intake manifold passage plugging up with carbon and oil. The EGR valve has to be removed and the passage cleaned thoroughly. Partial restriction of this passage can cause Smog test failures for the NOx emissions without causing a drivability symptom.
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Repairpal verified 1994 Mercury Cougar problems
While steering, if you hear a clunk or a rattle, or if you experience premature tire wear, this could indicate the inner tie rod ends are loose or worn and will require replacement.
Engine misfire could be caused by worn or broken motor mounts that raise the motor on one side while the vehicle is accelerating. The stress on the engine control wiring harness can cause breaks in the injector or sensor wires, which then causes driveability concerns such as poor fuel economy and engine misfires.