Hi guys. i was driving on the highway today and noticed thick smoke from my exhaust. a little later the engine started to shake and felt like it was going to give out plus the same smoke, then the check engine light came on. i called my mech and he said just put in a higher grade gasoline, i did and the CEL light went off but the engine still shakes with exhaust smoke when u accelerate past about 100kph on the highway. can anyone help with this PLZ?? btw i only have like 30K (AT trans 2.0 sedan) thanks a lot!