took my car to pep boys 4 times over the last month...replaced alot of things, etc.. however the service engine light keeps coming on and they can't figure out why...they have run several diagnostic tests and everything looks fine. they think a piece of carbon may be stuck "somewhere" in the system. they have checked all fuel and emissions systems and all looks good. does this "piece of carbon" stuff sound like BS? anyone have any suggestions besides pep boys being a "rip off!" thanks everyone!