Possibly an issue with the amount of air getting into the engine? Check that there isn't an air leak after the MAF in the intake. Also check that the air filter is in good condition. That's just a start.
I almost feel stupid for taking up space in these forums for this issue, but here goes: Code 0172 & 1175 (system too rich) turned out to be gas cap not on properly. Owner's manual did say that could be a cause of "check engine soon" light.
Have put appr. 40 mi. on veh. since clearing the code and tightening gas cap, no "check engine soon" light. Hope that was all it was!