My 2001 Accent GSI has had a slight bog/hesitation when accelerating at low revs or under high load for some time. In the last two days, the problem has worsened to the point that the car idles roughly, and feels like it is running on 3 cylinders in the lower end of the rev range. Also, it is now displaying a flashing check engine light. The poor running has coinsided with a dramatic increase in temperature in my area.

I pulled the MAP sensor, and found that it was covered in a film of oil. Also, there was a noticable puddle of oil in the opening in the intake surge tank where the MAP sensor plugs in. I imagine that this is likely a case of a bad PCV valve allowing oil up into the surge tank?

Could the oil on the MAP sensor be the cause of the uneven running? If so, will this necessitate replacement of the MAP sensor, or is there a method of cleaning it?

As an aside, I checked all four plugs, and number 4 (far right when facing the engine) seems to have more carbon/residue build up than the other 3. I have yet to obtain the codes from the ECU, but I imagine that several will have been tripped by the uneven idle and revving.

mine had the same problem i replaced the plugs and wires and set the gap on the plug, and all the hesitation went away. might wanna clean out your intake too, that will help alot.

the oil on the sensor well i dont know what that could be...sorry.