"Check Engine" = Map Airflow Sensor

[MyLegacyIsDoomed]

my '96 legacy wagon recently had the "check engine" light come on. we brought it in for a diagnostic and it came up with something like "MAP Airflow Sensor". i'm reading on here something about MAP Sensors being on 2000+ models. i also inquired about purchasing a new sensor from the dealer and it was a whopping $300.00+...yikes!!! anyone know a place in southern california (or online) where i can purchase one for less dough? i am told this sensor can be slightly off for it to act up, but nothing really significant is wrong with the car...but please correct me if i'm wrong.

[ferret]

There are MAP's and there are MAF's. Subaru has used both. Not sure what you have, But:

 

MAF - Manifold Air Flow Sensor, usually mounted in the Air intake after the air filter but before the throttle body. These usually have the Air filter mounted on the inner fender. These are small thin dissimiliar wires that measure the air flow density by the resistance measurement between the different elements. Usually any contaminient (oil, dirt, etc) upsets or damages it. If you have a MAF, I would try to remove it and carefully clean the wires with a q-tip and isopropal alcohol. Ebay many times has used good ones cheap.

 

MAP - Manifold Air Pressure is a sensor mounted on or behind the throttle body exposed to the intake vacuum. Here the Air filter can be mounted directly on the throttle body If space permits. This uses a barometric type sensor to measure the air pressure within the manifold. This type sensor is a little more rugged.

 

Either work with the ECU with the engine temp sensor and throttle position sensor to help generate a gross fuel trim (combustible mixture). The fine fuel trim uses the Oxygen sensor and feedback method to further control emissions. This is why cars will run in 'open loop', without oxygen sensor feedback, but will fail to even start without a MAF or MAP input.

 

I know...more that you need to know or asked, but I the words were just in the right place at my fingertips today.

[mwatt]

my '96 legacy wagon recently had the "check engine" light come on. we brought it in for a diagnostic and it came up with something like "MAP Airflow Sensor". i'm reading on here something about MAP Sensors being on 2000+ models. i also inquired about purchasing a new sensor from the dealer and it was a whopping $300.00+...yikes!!! anyone know a place in southern california (or online) where i can purchase one for less dough? i am told this sensor can be slightly off for it to act up, but nothing really significant is wrong with the car...but please correct me if i'm wrong.

 

You'll probably save a considerable amount by going to 1stsubaruparts.com

They're actually a Subaru dealer in Washington. There's a toll-free number listed on the website; you can contact one of the parts counter-people and specify that you want to purchase parts thru 1stsubaruparts.com

They will look up the part for you. Great service. Yes, there's a shipping fee, but you'll still save bucks.

[1 Lucky Texan]

There are MAP's and there are MAF's. Subaru has used both. Not sure what you have, But:

 

MAF - Manifold Air Flow Sensor, usually mounted in the Air intake after the air filter but before the throttle body. These usually have the Air filter mounted on the inner fender. These are small thin dissimiliar wires that measure the air flow density by the resistance measurement between the different elements. Usually any contaminient (oil, dirt, etc) upsets or damages it. If you have a MAF, I would try to remove it and carefully clean the wires with a q-tip and isopropal alcohol. Ebay many times has used good ones cheap.

 

MAP - Manifold Air Pressure is a sensor mounted on or behind the throttle body exposed to the intake vacuum. Here the Air filter can be mounted directly on the throttle body If space permits. This uses a barometric type sensor to measure the air pressure within the manifold. This type sensor is a little more rugged.

 

Either work with the ECU with the engine temp sensor and throttle position sensor to help generate a gross fuel trim (combustible mixture). The fine fuel trim uses the Oxygen sensor and feedback method to further control emissions. This is why cars will run in 'open loop', without oxygen sensor feedback, but will fail to even start without a MAF or MAP input.

 

I know...more that you need to know or asked, but I the words were just in the right place at my fingertips today.

 

this should be 'stickied'!

 

thanx

 

Carl

[avk]

What was the actual code?

[Commuter]

Just one other caution.

 

I discovered a few years ago that my 97 OB with automatic has a sensor that they call "MAP", but it is not the one described above. My car uses a MAF for the air to the engine. The other sensor was listed as "Manifold/Atmospheric Pressure", or something like that. It is a small black little item mounted on the passenger strut tower. It has a vacuum line running to the throttle body. I was told that this sensor keeps tabs on the vacuum in the manifold and atmospheric pressure and that this is some sort of input to the automatic transmissions shift algorithm. I discovered that mine had gone faulty when I started to get an occasional CEL that came up with the EGR code. What do these 2 have to do with each other? Apparently, this "MAP" sensor has a secondary function in that it looks for a change in manifold vacuum when the EGR valve is opened. If it doesn't see it, an EGR failure code is set. In my case, the EGR was actually ok, but the sensor was failing.

 

There was one other side effect from this failing sensor - slightly soft/delayed shifting. I was noticing this now and again. That problem disappeared once the sensor was replaced. Final note - e.x.p.e.n.s.i.v.e little sucker.

 

I don't know if a code can be directly set by this sensor, or what that code/description would be. No idea on that one.

 

FYI

 

Commuter

[MyLegacyIsDoomed]

thanks for the replies and all the great info...although now i'm more confused...LOL.

 

the diagnostic device definitely had the word (or acronym) "MAP", not "MAF" in it. however, the mechanic was pretty adamant that is was the Mass Airflow Sensor. but, then again, this was the bozo who thought my battery or ignition switch caused my last dilemma...many $$$ dollars later, it turned out to be the alarm...so, i'm not too confident in his diagnosis. and now that i'm reading what you guys are describing, it makes me even more skeptical of his accuracy.

 

so where does this leave me? do i buy a new MAF or MAP? i'm still not sure i understand what i need. does anyone have links to descriptions/photos/etc. that would be the most helpful.

 

thanks again...

[Setright]

Ermmm, it's actually Mass Air Flow, because the unit can deduce how many kilograms of air are passing through it.

 

 

The Manifold Air Pressure can't do that alone, it needs the temperature sensor help interpolate the mass of the ingested air.

 

 

MAF is more accurate and more expensive. And yes, a little fragile.

[avk]

Please read the code if it's still active, or in the memory, and post it.

[soobyfan]

I recently has a similar problem on my '96 OBW, 2.2L. I have a scanner so I can read and reset my own codes, it had code #106, indicating the manifold pressure is out of range. Anyway, my software allows me to look at the engine parameters while it is running, and I noticed the manifold pressure was 29.95 in/hg at idle. I knew that could not be right, so I looked around under the hood and sure enough, a small vaccum hose was disconnected. Hooked it back up, cleared the code and everything was back to normal. The manifold pressure at idle is about 10 in/hg.

[blitz]

does anyone have links to descriptions/photos/etc.

This one's pretty good:

 

http://www.cobbtuning.com/tech/airflow/index.html

[friendly_jacek]

Before shelling big $$$ for new MAF one should try cleaning it first (but very gently). Also, good mechanic knows that sensor connector problems are almost as common as sensor failure itself.