With the engine off, get a rag and throttle body cleaner spray that is sensor safe(crc). Clean out the tbi real good, Gunk is the enemy!
I do recommend against oil soaked air filters, and so does GM! MAF can look clean and still be out of range, a scan tool that reads live sensor data will help here. Maf testing: On GM MAF sensors, there's a couple of quick checks you can do for
vibration-related sensor problems. Attach an analog voltmeter to the
appropriate MAF sensor output terminal. With the engine idling, the
sensor should be putting out a steady 2.5 volts. Tap lightly on the
sensor and note the meter reading. A good sensor should show no change.
If the analog needle 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 30 to 50 Hz at idle and 70 to 75 Hz at 3,500 rpm. The
later model units (like those on a 3800 V6) 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
On the GM hot film MAFs, you can also tap into the ALDL data stream
with a scan tool and 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 throughout the rpm range. 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 it's output
changes appropriately. This can be done by graphing its frequency
output every 500 rpm, or by observing the sensor's waveform on a scope.
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
Thursday, December 30th, 2010 AT 4:46 PM