I have a 1998 Mercury Mystique, 2.0L Zetec Automatic. The car runs perfectly most of the time. Periodically, say once or twice per week the car will start bucking violently, (as if I were towing someone and they kept slamming on the brakes). At lights and stop signs the engine will sputter and occassionally stall. Usually if I horse it a bit, the problem will go away but not always. I have tried to look for arcing at night but see no signs of any. I do have a check engine light that reports a faulty cam sensor. I have replaced the sensor but the light comes back. After a few days of not happening the light turns off. A few days later it will start bucking again. There does not seem to be a pattern to this behavior, be it rain or cold or heat. The only thing that "sometimes" helps is letting the engine warm up for 15 minutes before leaving with it, (but this usually makes the check engine light come on faster).
Any ideas?
