My car has been acting kinda funny and i am just seeing what you guys imput is. Everytime i start the car it idles alil higher now about a lil ver 1k and when i start to drive it hesitates and then goes and hesitates then goes and does not shift right away. then when it goes away about a mile down the road the check engine light comes on when its driving fine and will go off and on.. I recently went up to the track and put 110 in my car 2 gallons with 4 gallons of 93 and thats when this problem started happening.. Could adding that race fuel be the cause of it? I have a 95 z28 with only a, hypertech, flowmaster cat-back and k&N cai and a a4 with 2400 stall