MAF readings leave me asking "huh?"

[huh?]

1997
3.0L
manual trans/auto trans computer


out of the blues my 97 3.0 starts bucking throughout the throttle range. the long term fuel trim for both banks would stay in the -10 to -25 range, depending on acceleration conditions. i originally was trying to trouble shoot using only fuel trim info till a code relating to the MAF sensor being out of range showed up. when i scrolled down to the MAFlbs/min on the live data screen i saw the normal(to me) 0.7__ at idle. when i hit the throttle the reading momentarily dives to 0.2__ then as i drive along with a steady throttle and road speed the display will go something like:

3.294
1.432
4.659
0.338
0.237
12.452
7.534
3.156
2.559
2.600
14.783

and so on.

cleaned the MAF sensor and IAC valve. runs a little smoother maybe at idle but drivability is still poor. no change in the range or randomness of the lbs/min displayed in the live data.

under load, such as driving up the hill to get home or stomping the throttle to merge into traffic, every few seconds the rattle of detonation comes through clearly.

what is the most likely cause:

1- MAF sensor itself;

2- the circuit that services the MAF sensor;

3- the PCM; or

4- i'm way off base. i should have used the torque wrench the last time i changed my right rear tire to avoid this situation.

 

[97RangerXLT]

4. definitely #4.

I would try swapping out the MAF sensor itself, sounds like it is taking a dump. definitely cheaper than replacing the pcm. before changing it, double check all of the connections to it and to the pcm...

you can probably get one from the junkyard for a few bucks, hell get a couple. if you get the same results with 3 or more MAF's you will know to look further.

AJ

 

[fastpakr]

You can also directly probe the MAF as you change RPM. Assuming it has a good 5v reference and solid ground, then if it's not changing progressively with throttle it's definitely bad.