normal tank mileage 360-380. bought some bad gas and got 245 miles that tank. car running bad. white smoke coming out of exhaust. idledrops drastically when stopped with foot on break. hesitation when touch gas pedal. got new tank of gas (high octane) went 51 miles on 6 gallons of gas. changed plugs and oil. noticed gas smell in oil. inside car smells of unburnt fuel when running. think possible injector stuck but not sure how to check. please advise any info.