The car is running rich for some reason. You may have bad injectors that are leaking excess fuel into the combustion chamber. Also, you could have a bad oxygen sensor that is telling the engine that it is running lean, when it actually is no. This causes the computer to send extra gas to the engine to make the air/fuel ratio correct but instead it makes it too rich because the oxygen sensor has sent the wrong signal.
You may have other issues as well with so much mileage. I am including a walk through diagnostic for your situation. Just use the link below to get to it;

http://www.2carpros.com/articles/engine-misfires-or-runs-rough

Answered by DrCranknWrench (expert)
3,292 answers provided