the lh 2.4 cars have adaptation, or learning, built in. that's why code 113, 231 and 232 are in the self diagnostics. they set when the range has been exceded. i've had 2 cars learn bad habits through adaptation and run so bad, they fouled the plugs. 1 needed a new amm because it would go out of range after 200 miles in 1 trip. the other needed a new ecu because it was demented and fouled the plugs for no outside reason. of course, it spit codes out like candy 1 or 2 times a month and ran so bad, it wouldn't start. it's possible yours has adjusted to the climate and fuel available. good luck, chuck.