Sluggish performance, worsens as the calibration gets worse. It is a slow drift, so it is hard to notice getting worse over time. My customers report that a MAF rebuild really wakes up the performance, car just feels more responsive.

If the MAF is too far out of calibration, especially the pre-1987 928s, it will fail emissions tests. If really far enough out of calibration, a MAF will cause a no-start condition.

I test 928 MAFs and advise the state of calibration and if a MAF rebuild is needed.

Rich
'93 GTS Cover Girl
'87 S4
'79 5-speed rescue
'79 928 5-liter track beast

 

Slow degradation can be held off by adjusting the A/F pot to compensate, until the point where the car goes into "limp-home" mode. Then it's done.

You'll know if you're in limp home mode. The LH brain assumes the MAF is dead and sets the fuel rate at a constant designed to run "OK" at 2500-3000 rpm. Above that, stuttering, loss of power and just general bad running of the engine. You'll know it if you're in limp home mode, it is not a subtle change. A simple check is disconnect the MAF plug and drive the car. You'll be in limp home mode then. If you notice a distinct difference your MAF isn't completely dead yet. If you don't notice a difference then your already there.

The "Open loop" MAF in the pre-86 Euros is a ticking time bomb, but it goes out with a whimper not a bang. Whoever said it should be treated as a consumable wasn't too far off.

Just my experience...

 

as I suggested the MAF going out of calibration will cause poor running and stumble and possibly no idle conditions in the early 84/85 Euro engines.

Fitting a fresh calibrated MAF makes the fuel injection system run as it was designed,
since the Euro cars dont have an O2 sensor the MAF is responsible for running mixture