MAF sensor Bad?

TESTING
MAF sensors can be tested either on or off
the vehicle in a variety of ways.
You can use a MAF Sensor Tester and
tachometer to check the sensor’s response.
If testing on the vehicle, unplug the wiring
harness connector from the sensor and
connect the tester and tachometer. Start the
engine and watch the readings. They should
change as the throttle is opened and
closed. No change would indicate a
bad sensor. The same hookup can be
used to test the MAF sensor off the
vehicle. When you blow through the sensor,
the readings should change if the sensor is
detecting the change in air flow.
Another check is to read the sensor’s voltage
or frequency output on the vehicle. With
Bosch hot-wire MAF sensors, the output
voltage can be read directly with a digital
voltmeter by back probing the brown-and white
output wire to terminal B6 on the
PCM. The voltage reading should be around
2.5 volts. If out of range, or if the sensor’s
voltage output fails to increase when the
throttle is opened with the engine running,
the sensor may be defective. Check the orange
and black feed wire for 12 volts, and the
black wire for a good ground. Power to the
MAF sensor is provided through a pair of
relays (one for power, one for the burn-off
cleaning cycle), so check the relays too, if the
MAF sensor appears to be dead or sluggish.
If the sensor works but is slow to respond to
changes in air flow, the problem may be a
contaminated sensing element caused by a
failure in the self-cleaning circuit or relay.
With GM Delco MAF sensors, attach a
digital voltmeter to the appropriate MAF
sensor output terminal. With the engine
idling, the sensor should output a steady 2.5
volts. Tap lightly on the sensor and note the
meter reading. A good sensor should show
no change. If the meter reading jumps and/or
the engine momentarily misfires, the sensor
is bad and needs to be replaced. You can
also check for heat-related problems by
heating the sensor with a hair dryer and
repeating the test.
This same test can also be done using a
meter that reads frequency. The older AC
Delco MAF sensors (like a 2.8L V6) should
show a steady reading of 32 Hz at idle to
about 75 Hz at 3,500 rpm. The later model
units (like those on a 3800 V6 with the
Hitachi MAF sensor) should read about
2.9 kHz at idle and 5.0 kHz at 3,500 rpm.
If tapping on the MAF sensor produces a
sudden change in the frequency signal,
it’s time for a new sensor.
On GM hot-film MAFs, you can also use
a scan tool to read the sensor’s output in
“grams per second” (gps), which corresponds
to frequency. The reading should go from
4 to 8 gps at idle up to 100 to 240 gps at
wide-open throttle.
Like throttle position sensors, there should
be smooth linear transition in sensor output
as engine speed and load change. If the
readings jump all over the place, the computer
won’t be able to deliver the right air/fuel
mixture and driveability and emissions will
suffer. So you should also check the sensor’s
output at various speeds to see that its
output changes appropriately.
Another way to observe the sensor’s
output is to look at its waveform on an
oscilloscope. The waveform should be square
and show a gradual increase in frequency as
engine speed and load increase. Any skips
or sudden jumps or excessive noise in the
pattern would tell you the sensor needs to
be replaced.