Drove off to work the other day, got about 300 feet from the house and the engine died. Rolled it to a stop, and tried to restart the engine. Starter would turn, but the engine wouldn't stay running.

Left the key in the ignition in the ON position for a few moments while I checked the engine codes (I have a Scanguage II hooked up to my OBDII port). The code read back as a fault with the Mass Air Flow Sensor.

Further testing indicated that the engine would start and stay running if the electronics and pumps and whatnot were given a few minutes to warm up in the ON position before the key was turned to the START position. I drove the car to work, and confirmed that the symptoms still existed during my lunch break, my trip to the gym, and then before my drive home. Car would not stay running from a cold start, but would start and run normally if given a few moments to "warm up" the electronics.

When I got home, I removed the mass airflow sensor and cleaned it out with a few bursts of electronic parts cleaner. I reinstalled the sensor, cleared the trouble codes, and the car seems to be running fine for the past week.

Turns out that the mass airflow sensor uses a thin wire that is heated to measure the amount of air required to keep the wire cool. Over time, the wire can accumulate dust, soot, and oil, and trick the sensor into thinking that the airflow is restricted and will cut fuel. (No air, no fuel, no combustion).

Cleaning or inspecting the MAF is not listed as a regular maintenance item, but I think I'll add cleaning it out to my 30k or 60k service.

My car was at exactly 120,010 miles when it started acting up.

That would not be good if you were on the interstate with no pull over lanes. Looks like the engineers should have added a warning light.

What's a mass airflight filter?

Just did it on my wife's Forrester at 60k along with plugs, filters and oils. Her MPG dropped about 2 mpg over the past few months. All those changes did nothing!

Mid 2000's we had a GM TSB warning against using K&N Air Filters because of potential MAF failure due to over oiling the filter.

quote:

Originally posted by shovelhead:
Mid 2000's we had a GM TSB warning against using K&N Air Filters because of potential MAF failure due to over oiling the filter.

This can happen with any brand with those junky oil filters. They make a mess and they don't filter as well.


Para,

A MAF is installed in the intake tube behind the filter to measure airflow and air temperature entering the engine so the computer can adjust fueling accordingly. It's an expensive part so be careful if you feel inclined to clean it.

Yes. Although it was running just fine the check engine light came on in my 04 Tundra around 40,000 miles. I couldn't read the code but my friend said it was likely to be the Mass Airflow Sensor. Bought the cleaner spray at Auto Zone, cleaned it, and end of light.

quote:

Originally posted by parabellum:
What's a mass airflight filter?

Images of various mass air flow sensors They are mounted between the air cleaner and the engine intake. Most cars have them these days.

I had an older Ford Explorer that wouldn't even start, though it had everything typically needed to run, i.e., spark, fuel, compression and injector pulse. The owner even replaced the fuel pump - needlessly and not an easy job on that vehicle. But it would start when I disconnected the wire from the MAF sensor. Turned out a spider had gotten past an improperly installed air filter, into the sensor and gotten fried. Cleaning it got it to run. It did NOT have a code for the sensor. It takes the wire being disconnected or other loss of power to do that. It was just far out of range.