Is there a program feature in the ECU that can effect lean or rich mixture. I have new or good 0 and knock sensors all around but mileage is at a unusual low. Could an evil mechanic with the code box have made an adjustment to cause a richer mixture that would not reflect with a code? If so, is there a manual read or reset method? thanks.

 

No. Have you had a regular tune up, plugs, filters, fliuds? Are your tires properly inflated? Have you cleaned your TB and EGR?

 

The plugs have under 50000 miles, everything else is ahead of schedule, clean and i replaced the egr due to a code early in 2012. The mpg seems have dropped off soon after i replaced the front 02, but, i have no residual codes indicating any problems with any of the sensors. Engine at 215k-km. Been very cold here and I let the engine warm up or idle longer than usual, but not enough to effect things drastically in mpg.

 

Cold weather where you live? I am on my phone so not all of your screen name info is visible.

 

Ottawa, Canada. -17C at the moment, been -25 to - 30 for a week, but my issue has been months.