I'm chasing a PO171 problem and have a scan tool. According to some information I've read, the idle MAF number in grams of air should be about the same as the engine size, i.e. 2.3 grams/sec for my 2.3.

I've graphed the MAF with my scan tool, and at idle it runs about 3.7. + or - about .2. This seems excessive and makes me think it could be the source of the PO171. Can someone with a scan tool (or knowledge) advise?

I've installed a new air cleaner, cleaned the MAF sensor with the CRC stuff, and assured that all hoses are connected and clamps tight. I also cleaned the MAF sensor electrical connection and put a dab of dielectric grease inside.

Thanks for looking.

 

Yes, the displacement and gm/sec should be about the same, but that is also assuming 650-700 rpm idle, so warmed up engine.
Higher RPMs would, of course, mean higher air flow.

Cold engines often idle above 1,000

The 2.3l, like many 4cyl engines, often idle at 800, or higher on automatics, even after warm up.

And a false higher air flow would cause P0172(rich) not P0171(lean)

For example:
Computer would add enough fuel for 3.7 gm/sec, if this was a false high reading and air flow was really 2.7 gm/sec then computer is adding too much fuel.
When air/fuel mix is burned O2 sensor would report less oxygen(rich), so computer would reduce the amount of fuel it is adding, "-" fuel trim numbers, like -10 STFT
If it gets to -20 STFT then computer will set P0172(rich) and turn on the CEL

Lean code is when less air is reported by MAF sensor, usually because of a vacuum leak, not all the air coming into engine is coming thru the MAF sensor.
So at idle you might see, 1.5-2 gm/sec, when it should be 2.7 gm/sec, so computer is adding less fuel than it should, after it is burned O2 shows too much oxygen so computer adds more fuel, "+" fuel trims, when +20 STFT is seen then computer sets P0171 code, Lean

 

Thanks yet again, Ron. Would you like to visit Gilroy and stay in my spare bedroom for a couple of weeks?

 

Is that Old Gilroy or Gilroy, lol.

I grew up in southern cal, driven up 101 more than a few times, I remember the road from Salinas over to Gilroy as very beautiful, probably a 6 lane freeway by now

 

It IS 6 lanes now (old 101 bypassed Gilroy in 1985) but it's still beautiful, and still smells like garlic. :-)