I have a 2008 Dodge Caravan and recently took it to get its oil changed. These guys are usually very good about not trying to sell all those little extra money-makers, but this time they said that when they took off the air filter cover they found grease in the throttle body, and suggested a $90.00 fuel system cleaner. Well, I'm no expert, but I don't think the throttle body is under the air filter cover, so I put them off. My question - do I really need to clean my fuel system regularly? If so, is it something I can do myself?