MAP or MAF

I have a 2000 Alero with the 3400 that has approximately 180,000 miles. I have been working on a poor fuel mileage problem over the past few months, during which time, I have replaced the plugs, wires, front O2 sensor, and fuel injector O-rings. It is running better, but it is still a little rough at idle. The mileage had stabilized at about 25 mpg in mixed driving. However, as the weather has gotten warmer in Michigan, the mileage has gotten progressively better. The last tank full was run during 60-70 degree weather and I have gotten just over 27 mpg on the same mixed driving. To me, it sounds like a MAF or MAP sensor is sending a default number to the computer, and now that the weather condition matches this default number, it is running normally.

Anyone else have any thoughts or theories on this phenomenon http://www.automotiveforums.com/vbulletin/images/icons/icon5.gif

Run it on a full function scanner and see what the results are. Especially check short and long term fuel trim. If the MAF or MAP sensors were out of range or had a performance issue I'm quite sure the PCM module would trigger the SES/CEL light and store a DTC(s).

The gas mileage figures, which is nothing to complain about, you are getting could be normal based on how you drive, weather and the driving conditions. I see an increase in mileage at this time of the year versus the winter.

Yeah, thankfully with the gas prices currently going through the ceiling...I'm also seeing an increase in fuel mileage back to my normal 26-27 mpg. :grinyes:

BNaylor, thanks for the response. I appreciate the advice. And don't get me wrong, I am not complaining about my fuel mileage. I was just hoping that someone knowledgable (like yourself), would be able to put the clues together to figure out what was going on. That, plus, I am really cheap and want to keep the good mileage when the weather turns cold again.