Is it diesel,Are there any symbols in the instrument panel. There is a possibility that the particulate filter may be causing problems. the symbol to look out for is like a coil of wire, constant or flashing. I had this, and it ran lumpy. In the book you are told to drive at constant 40 moh for up to 20 minutes, the symbol should go out. If it does not, see dealer, I believe that it can cause major problems if left.. Hope this helps.
I am not an expert, this is from my own experience.
Derek Maple
June 2009
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