well there are several things that could be doing this like the normal oil in the spark plug holes due to a leaky valve cover gasket, maybe just your spark plugs are old, fuel filter could be pluged, but I will tell you this one to try I was having alot of the same problems but mine was the mass air flow sensor $187 bucks from the dealer, alot cheaper online though. just unplug it next time your car is running bad and mis-firing and see if it runs alittle better, if it does that is your problem. your mass air flow sensor is on the inlet air tube after your filter housing. Ben