My Chevrolet Cobalt 2010 2.2 LT has been shaking and stalling when in idle. After reading multiple forums, I decided to try cleaning the throttle body. I took it off completely and cleaned it with throttle body cleaner. I also cleaned the air intake sensor with mass air intake sensor cleaner. After putting everything back on, the car displayed a message saying "engine power reduced" and it makes a clunking sound between 25-55mph. Any ideas on what could be the problem, one problem keeps happening after another! Thanks in advance!!

 

If you read the forums for cleaning the throttle body, you'll also notice that issues do arise after cleaning it since it's a fly-by-wire system. Have you tried the battery relearn method? Otherwise, you'll need to keep driving it (non-aggressively) until the system adapts to the carbon-less plate positions.
Another option is to have a dealership flash the ECU, although there hasn't been a lot of luck for that either.