mass air flow sensor noise

Greetings,
A friend of mine has a 1996 V6 Explorer. It has about 100,000 miles on it.
It is having a weird problem with the mass air flow sensor. Sometimes when
it is driving about 35 mph at light load (just cruising), or idling, the mass air flow sensor lets out a nasty buzzing sound. The one time I caught it doing it, it definately was in the tube that holds the mass airflow sensor, and I put my hand on it, and I could feel it vibrating.
I pulled off the sensor, and it appears to be in good shape (Ie there wasn't anything obviously bad with it). However, when I shook it, there was a bit of a rattle to it. I don't have another one to compare with it.
My presumption is that the inner metal tube part has unglued itself or something like that, and when the right amount of air goes through it, it hits some sort of natural vibration frequency and gets really, really annoying. This is an intermittent problem. It can drive for an hour without doing it, or it can do it within 5 minutes of starting. If it is doing it, and it is stopped, it will continue to make the noise while idling, but if the engine is accellerated, it will go away.
There is a problem with the NOx system as well (check engine light, with a 'too much NOx flow' and 'too little NOx flow' errors.
It also seems to be idling rough, and fast idling (about 1000 rpm), but I'm guessing that is part of the NOx issue. However, it has been known to have the engine actually die when the Mass Airflow Sensor is being noisy.
Another thing I noticed is that it idled terribly when the mass airflow sensor was disconnected from the air filter, which seems counter-intuitive. Perhaps there is a restriction in the intake tubes that it needs or something.
Any thoughts on the noise? Is there a way to fix it, or should he just spring for a new mass airflow sensor? The NOx issue I have heard is likely the differential pressure sensor, but because it is a constant issue it should be relatively easy for a mechanic in the know to fix it.
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There's really nothing in the MAF sensor that can emit a noise...... next time you get the noise, try unplugging the IAC - these have been known to vibrate and emit quite a loud noise (when we are driving, the IAC is supposed to go to full duty cycle and remain pretty much wide open).
Since the MAF is measuring the air mass entering the motor, there is little wonder that it will idle rough when the MAF is disconnected..... The PCM can no longer "see" how much air is entering the motor and will default to a preprogrammed strategy designed to keep the motor from self destructing due to lean mixtures and such.
I must assume that you are talking about EGR flow rather than NOx flow..... I'm going to take a stab in the dark and opine that the DTC retrieved was a P0401??? The DPFE sensor lives in a pretty harsh environment and is a well known weak spot in the EGR system.
Jim Warman snipped-for-privacy@telusplanet.net

it.
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I think you misunderstood. I had disconnected the mass airflow sensor at the air filter side, but the rest of it was connected to the intake tube and wiring. So there should have been just as much air flow (actually slightly more than normal), and it just seemed odd that it would affect the engine performance. Granted that it isn't a good idea to run it that way.
Where is the the idle air control valve on the explorer? Would this cause a vibration that I could feel on the mass airflow sensor that went away when the noise stopped?
And yes, I was referring to the EGR system, which controls NOx.
Thanks.
On Mon, 16 Feb 2004 03:24:54 GMT, Jim Warman wrote:

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IAC is mounted close to the throttle plates....... cylindrical with a two wire connector. Running bad with the MAF out of the filter almost sounds like a red herring...... Is the filter stock paper or something I usually snicker about??? If it does run bad with the MAF moved, check the connectors..... it's always possible that a pin hasn't been fully seated before the lock was inserted...
After 8 years and 100K miles, it wouldn't surprise me to see more than one problem........ let's not forget that if the DPFE has confused the PCM or if the EVRV is leaking, the motor could run like absolute crap, anyway. Additionally, if this is a problem that has been lived with for any length of time, the excess EGR flow at undesired times could contaminate the IAC. It can be hard to form a diagnostic strategy with multiple concerns but it is much easier to progress from the easy/cheap to the hard/spendy and achieve what we need.....
Jim Warman snipped-for-privacy@telusplanet.net

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