Mass Air Flow Sensor 08/05/23
----------------------------------------------------------------------
I have two vehicles, one is 17 years old, the other is 23 years old.
I've always driven older cars, and I try to work on them myself, when
the repair is something I can tackle--when it's not, the car is
usually ready to get rid of.
The 2000 Chevy Impala has been running a little rough, and yesterday
morning it sputter out and died in the driveway. Real rough start, on
and off idling rough. My wife was very concerned, but I reassured her
that such a symptom isn't necessarily that big of a thing.
Did a little googling, and a bad Mass Air Flow Sensor (MAF) had
identical symptoms. I cracked the hood and removed the part; in this
vehicle, it's actually a very simple part to remove, without any need
to take apart the intake; two small bolts, and it slides out.
Didn't look that bad to me, but it's electrical and looks can be
deceiving. Our favorite wiki provides insights as to how the sensor
works:
"The theory of operation of the hot wire mass airflow sensor is
similar to that of the hot wire anemometer (which determines air
velocity). This is achieved by heating a wire suspended in the
engine’s air stream, like a toaster wire, by applying a constant
voltage over the wire. The wire's electrical resistance increases as
the wire’s temperature increases, which varies the electrical
current flowing through the circuit, according to Ohm's law. When air
flows past the wire, the wire cools, decreasing its resistance, which
in turn allows more current to flow through the circuit, since the
supply voltage is a constant. As more current flows, the wire’s
temperature increases until the resistance reaches equilibrium again.
The current increase or decrease is proportional to the mass of air
flowing past the wire. The integrated electronic circuit converts the
proportional measurement into a proportional voltage which is sent to
the ECU."[1]
Some MAFs have four or more "hot wires" in an array. Mine had only
two. They looked OK, but I decided to replace the part anyway, as it
was only ~$20 on Amazon. Of course, I needed to see what the local
parts stores had first...
Autozone had one in stock, but they wanted $128 for it. Silly, when
you look at the thing. O'Reilly's would have to order one, and they
wanted $84. My goodness... I probably would have paid $49 for it, just
to keep the local shops open, but $84-$128? And as for parts quality,
I've have excellent luck buying parts on Amazon over the years, so the
argument is tough. Oh well; I bought a new air filter from O'Reilly's
(Fram, $20--on Amazon you can get an off-brand one for <$10, but a
Fram on there is $17), to keep the local shops running, and went home.
The part from Amazon said it would arrive next-day. Fine, it is
ordered and should be here today. But with some time to kill, I
decided to just clean out the old one with alcohol, just for kicks. It
looked a little better when I was done. Threw it all back together,
reset the computer with a little ODB2 reader, and fired it up.
The engine ran great, better than it has in months. No codes (it was
throwing P0102 instantly before, after a reset). Drove it around, and
it was working great.
This morning, just for fun, I also opened up the 2006 Dodge Grand
Caravan, to see about the intake there. No MAF, just an air temp
sensor, which I cleaned for fun.
Long story short: a little bit of dust on a tiny hot wire sensor can
impact its resistance and make your car run like crap. A stalling out
car doesn't mean the engine is dead, or that you need hundreds or
thousands of dollars in repairs--sometimes it just means you need to
clean something.
[1]
gopher://gopherpedia.com:70/0/Mass flow sensor
