My 2010 cobalt has 136k miles. Husband says he heard an engine knocking noise but mechanic and I don't hear anything. Few weeks ago car lost power and I felt a pulsating/knocking vibration through the steering wheel while accelerating on the freeway, for 7 seconds or so, and then I regained power although the power felt a bit weak from time to time after that. A week later it happened again when I was accelerating up a slope, only this time CEL flashed at me for the 10 seconds or so; I couldn't go above 15 mph and then my car pulled out of the issue once more. The dealer found nothing amiss after the first incident. After the 2nd one, the dealer pulled a code(s?) and found shot spark plugs and 2 ignition coils that needed replaced. Well, $465 later and issue is occurring once more. This time I gunned the pedal at 50 mph, felt my engine lose power, CEL started flashing, and I turned around. Engine shuddered the entire time and barely stayed alive while I was stopped, waiting to do a u-turn to my nearby home. I have an appointment at the dealer tomorrow but am terrified they won't be able to get to the root of the problem. What does this sound like? Could it even be a bad engine mount, loose or disconnected hoses on or around the engine, VVT, timing chain, idle air control valve, MAF sensor air leaks, throttle by wire, bent valve, or other? How can I get my mechanic to get to the root of the problem? Should I take it to an indepdent mechanic instead of the dealer? Should I take it to Auto Zone first and get the codes read?