I have a 1991 Buick Skylark 3.3 engine with 57,000 miles on it. I drove it for about 30 miles after it sat without being driven for about six months and it was running bad. After I turn the engine off, the car won't start anymore. it turns good, but won't start. I sprayed starting fluid in the air cleaner inlet and nothing. I washed the engine to remove all the dirt from the engine with an water hose. What could it be?