Ozz

Need a little help here. For some reason the car starts missing and the tach drops to 0 the engine keeps running but no tach and I have missfires, then it smooths out and the tach comes back alive. This all started after I got a bad tank of gas one night. I added HEET and ran out a lot of the bad gas but there is still some left in it I am sure. I would blame it for the misfires but the tach makes no sense. Any help would be great.