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Subaru Mass Air Flow Sensor Problems

A mass air flow sensor (maf) is used in modern fuel-injected engines to sense the mass of combustion air entering the engine. The mass air flow sensor sends a signal to the engine control module (ECM) based on the mass flow of air. Based on this signal the ECM releases just the right amount of fuel for optimal combustion and to keep emissions to the minimum. A faulty mass air flow sensor has a devastating effect on an engine. Subaru mass air flow sensors often have issues with performance. When car owners face these issues they often have questions that need answered. Read below where Experts have answered a variety of questions about Subaru mass air flow sensors.

How can the MAF on a Subaru Impreza be cleaned?

Cleaners for this purpose are available at auto parts stores. You will have to spray them on to clean the sensor. If your sensor is giving a problem then check the wiring to it. Normally a code for the mass air sensor relates to the wiring or a break in the wiring. Checking the wiring first might be a better way to go.

On starting a Subaru Impreza where the mass air flow sensor was changed the oil temperature light flashes and the engine sends a maf code what could the cause be?

If after replacing the mass air flow sensor the code still remains, chances are that the issue is with the wiring to the sensor rather than with the sensor itself. Since the sensor works off resistance, the engine control module (ecm) will expect to see some resistance. As long as there is some resistance the ecm will not send a maf specific code nor turn on the check engine light. But if it reads no resistance a maf code is the likely outcome. Use a volt meter to check if the wiring is faulty.

A Subaru Outback is misfiring and the local garage says the mass air flow sensor has to be replaced which will cost $447 without labor. Could this be correct?

The spark plugs and wiring should first to be checked because they could cause misfiring. The CEL comes on for a number of reasons which includes poor engine performance and a bad mass air flow sensor. The on-board computer then sets a fault code which has to be read by a diagnostic scanner. Only when the diagnostic code is known can the real cause of fault be determined with any degree of accuracy. The way to go is to have the code read before touching the engine. Most auto parts stores do this for free.

The MAF and O2 sensors have been replaced on a Subaru Outback but the engine is rough when idling and tends to improve when past 1200 rpm. What could the problem be?

From the description it seems to be due to an air or vacuum leak. Open the hood and you might hear a hiss which could come from something as simple as a pin-hole leak in a vacuum line or hose. The other alternatives could be a plugged exhaust or faulty valve timing. Incidentally for this particular vehicle there was a mass recall on the mass air flow sensor. Try to find out if the MAF on this car was replaced during the recall.

Almost everything including the MAF has been replaced on a ’92 Subaru SVX but it still has no power when accelerating. What else could the owner do to resolve this problem?

1. Measure the fuel pressure at the injector rail while the engine is running. Even though the pump, filter and regulator have been replaced there could still be a problem here. A pressure of between 2.3 and 2.6 Bar is what it should be delivering.
2. Next check for an air leak - past the air flow meter - which is unlikely to be picked up by the ECU. Any leak would result in a lean mixture which will cause the engine to run rough. Check that all hose clips are tight and inspect the pipes and hoses in the vacuum system for splits and cracks. The best was to detect a leak is to spray gas lighter on each joint when the engine is hot and running. If there is a change in engine revs then you’ve located a leak.
3. The other things you need to check are the sensor connections to the coolant temperature sensor to see if they are corroded. If the sensor is faulty replace it because the ECU will adjust the fuel mixture to wrong inputs.

One of the biggest problems often blamed on mass air flow sensors are leaks after the sensor which it is unable to detect. These leaks result in a lean fuel/air mixture and consequent rough running of an engine. Before replacing a MAF consult an Expert because the cause could be something quite different.
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