bought van in 2007 for work. ran well. went out of business at end of 2007 and parked van. would start and warm up every month or so, no problem. Then about the last of August, 2010, it would not start. Found out that due to gas setting in tank for three years, had ruined the in tank fuel pump. Took tank off, cleaned out old gas, put new fuel pump, and new fuel filter on. Started and ran fine for a couple of weeks. Then found that would start and idle just fine but, upon acceleration it now has a terrible miss and seems to backfire through the air cleaner. Put new spark plugs in and another new fuel filter, of which neither has done any good. Please someone, HELP!