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Is my MAF out of spec or not?


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I've got a minor stumble at time when gently getting on the gas at low revs - it's not constant, it's not throwing up any codes, and it's not enough to throw money at either - I can live with it, but it's annoying...

I think it may be the MAF, but I'm guessing in all honesty. I've cleaned it thorougly, and the car does seem a little better for a shiny clean MAF in general, but it didn't affect the stumble. I've cleaned the throttle body, including removing it and cleaning it from the back, which made no difference. I've also replaced the AOS, and although that seems to have significantly reduced - almost stopped - the "clouds of smoke on startup" incidents and the car no longer stumbles and almost dies when the oil filler cap is removed, there is still a sucking sound from the cap when removed. I did the trick of removing the return pipe from the AOS to the throttle body and plugging the hole - no sucking noise, but quite an "overpressure" (perhaps because I plugged both the hole in the throttle body and the end of the return pipe).

Anyway, I've just checked the voltages on the MAF. When not running, they are 0.95v at pin 5 and 1.2v at pin 1, when idling they are 1.2v at pin 5 and 2.5 at pin 1. (5 is the air flow, 1 is the temperature, right?). Are these what I should expect? I doubt they are very far out, because as I say, there are no CELs or codes, and it's a *slight* stumble...

Many Thanks!

Graham

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I think you need to look at the MAF with the Durametric software, a PST2 or PIWIS tester to see what it is doing at idle and at 2500 RPM - no load.

Those numbers will tell you if it is working right or not.

Thanks Loren - I just ordered the OBD-2.com software (I've got vehicles OTHER than Porches :P ) but I'm guessing all that will really do is confirm my voltage readings, not tell me if they are in or out of spec.. Will the Durametric do that?

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I think you need to look at the MAF with the Durametric software, a PST2 or PIWIS tester to see what it is doing at idle and at 2500 RPM - no load.

Those numbers will tell you if it is working right or not.

Thanks Loren - I just ordered the OBD-2.com software (I've got vehicles OTHER than Porches :P ) but I'm guessing all that will really do is confirm my voltage readings, not tell me if they are in or out of spec.. Will the Durametric do that?

Both should be able to give you your air flow readings in kg/h (not voltage).

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