Please help! 1998 sl 500 was stored all winter. Started intermintently but not regular enough I guess. Charge battery and start. RUNS ROUGH..chugs like a train..low level boom ..sounds like a quiet but deep drum and seems to want to backfire. NO throttle response at all from the gas pedal. Could a computer have fried when I hooked up the battery again? Water in gas ? I used stabilizer before storage...in an insulated but not really heated garage. Suggestions PLEASE..