I was having issues with my 99 grand prix. narrowed it down to the maf by tapping on it and it was erradic on the scanner graph. I replace it.
everthing seemed fine for a week and the problem seemed to reapear.
I could tell the new sensor was a remanufactured one because the top looked like it was reglued on.
I read on the maf troubleshooting post in this forum that the output signal sould be at about 2.5 volts with 2.5 to 5.5 khz output a the sig wire which I probed at the input of the PCM so I know I dont have a harness problem. Well the frequency is varying accordingly with throttle positioning in that range but the voltage output from the maf is only .9 volts and not changing according to fluke the fluke. I am getting no reading on my scanner on the graph for the maf just a straight line
and engine is running erradic.
All other sensors are showing up on the scanner. I am suspicious of the new (reman) maf could be defective. due to the low voltage output of the sig wire.
does this sound reasonable anyone had this trouble before?

Have you tested it by disconnecting it?

Engine off, disconnect MAF electrical connector.
Start engine, observe idle. Does it idle better than it did with the MAF plugged in?

oh yea thats kinda the troubleshooting I did to find the original problem.
it stumbles a little on acceleration from Idle but it idles smooth after it settles down or at a steady rpm.

MAF is the culprit then.

ok thanks I was wondering if the output voltage was low
acctually I told you wrong the problem still exist becaust the voltage from the maf is not enoug for the pcm to read I think so when I disconnect it acts the same because of low voltage

It really shouldn't act the same. What the PCM does when it sees the MAF missing is, it reverts to a predetermined set of values based on cylinder air mass, along with a bunch of other techno babble. Or in other terms, "limp home mode".

Mike
The reason it dosent act diff pluged in or unpluged is because the pcm dont see cause it aint workin.
Ok so the maf signal output voltage is .9 volts at idle and it never changes due to rpm. I read where the sensor lead is supposed to vary from idle .9 volts to 2.5 at high rpm. It has the proper freq output about 1.5 khz to 5 khz but the voltage never changes. The power supply is good going to the maf
Im wondering about the sensor output voltage.

I thought the PCM was only concerned about the khz reading and not the voltage?

the best way to look at it is with a scanner that will show you live data, or monitors like the torque app, that way you know what the pcm sees.