I've got a 2007 SC Cobalt that keeps going into Reduced Engine Power mode. First time it did it the DTC was P1681. I replaced the throttle body with a new one shortly before it threw the timing chain and bent the valves. I replaced the valves and chain and then it started going into Reduced Engine Power mode again. First time I checked DTC's it had P0171 P2135 and P2119. I cleared these and a day later it set DTC's P2135 and P1681.

Does anyone have any ideas or the diagnostic flow charts for P1681?