This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.
The mass air flow sensor (MAF) is located inside the engine compartment and is used to measure the amount and temperature of air that is entering the engine at any one time. Older style meters used on fuel injection systems in the 1980s measured air volumetric flow, which worked fine but then you also needed a separate sensor to figure out how cold or dense the air was. The mass air flow sensor senses the total amount of air passing the sensor and allows the fuel injection system to adjust the fuel mixture to compensate for cold weather and/or high altitude conditions. The MAF also incorporates an internal intake air temperature sensor which measures the temperature of the intake air.
The first indicator that you might have a problem with the MAF is the presence of a check engine light (CEL) on your dashboard. The check engine lamp can be caused by a wide variety of problems with the engine: you need to read the codes from the computer to get a starting clue as to what the problem is (see Project 20 for details on reading the codes). It's perfectly safe to continue to drive the car while the CEL light is on, as long as it is not flashing. However, the engine will not be operating at peak efficiency, and you will most likely experience a loss in power and a decrease in gas mileage as a result. It's best to get the problem taken care of relatively quickly, as running the engine in this condition can potentially cause damage to other components like the catalytic converters.
The computer will know if something is wrong with the MAF because it will compare the values being output by the sensor to "expected"' values that it should be receiving. This common-sense check by the computer helps to diagnose problems with every component in the system. If the MAF becomes dirty and is falsely indicating to the engine that the car is receiving very little air while at full throttle, then the computer will most likely kick back an error code.
To gain more information about the problem, you can try disconnecting the sensor completely and taking the car for a drive. If you take short drives (30 minutes or less) with the sensor disconnected, it shouldn't cause any major damage to your car. The engine management system (DME) will enter into a type of "limp mode" that will compensate for the missing MAF. If engine performance improves dramatically when disconnecting the MAF, then the problem quite likely lies with the MAF.
Vacuum leaks and other air leaks in the system can cause MAF sensor errors. If you have a crack or leak in your air intake downstream of the sensor, then the MAF will be sensing less air than the engine is actually receiving. If the clamp on the throttle body happens to come loose and fall off, then the MAF will indicate almost no air being sucked through the intake, yet the engine will be sucking air directly from the engine compartment into the throttle body. The bottom line is that you should carefully inspect all of your hoses, clamps and intake tubes for air leaks prior to replacing the sensor (see Pelican Technical Article: Troubleshooting Vacuum Leaks).
The MAF is located on the left side of the engine compartment, just behind the air filter (see Project 3 for access to the engine compartment). For some reason, Porsche made it unusually difficult to remove the MAF, by securing it with a T20 tamper-proof Torx screw. You need the special tamper-proof Torx drivers which are not typically found in everyone's toolbox, but usually can be purchased at a good local auto parts store. Although the holes on the MAF look symmetrical, they are not and the unit can only be installed in one direction. See Photo 1 for a close-up of the MAF. Removal is easy, once you have the tool. Simply remove both screws holding it in place and pull it out. Boxsters from 2005 and later have a MAF with an integrated housing: simply unclamp the housing from the intake tube and remove it.
It's very important to keep the sensor clean. If the air cleaner isn't working too well, it could allow dust and debris to collect on the MAF. If you've had a problem with your air-oil separator, it could have contaminated the sensor as well. Oil sucked into the engine intake from a defective separator can easily find its way back to the intake tube. If you have had major engine problems (like our project car with the blown up engine), then you may find a ruined MAF. On our donor car, the MAF was soaked in oil and coolant residue that had found its way all over the engine. If you have an aftermarket reusable air filter, beware of how much cleaning and filtering oil you use on it. Excess oil may get sucked into the intake and find its way onto the MAF. To keep your MAF healthy, I recommend changing or cleaning your air filter often (see Pelican Technical Article: Air Filter / Pollen Filter Replacement).
If you are replacing your sensor, it is extremely important that you get the proper one for your car. There are two basic types, one for the cars that use a traditional throttle cable (up to 1999), and one for cars with an E-gas electronic throttle (2000 and later). In addition, the later-style E-gas sensor has been updated at least twice as of this moment. Porsche updated the sensors in the Boxster in mid-2000 and also released a new version of the DME software that is a required update if you are going to use this new and improved sensor (see Porsche Tech Bulletin Boxster 1a/00 2445). Here is a chart that shows the differences between all of the sensors:
|Porsche Part #||BOSCH Part #||Application||Notes|
|996.606.123.00||0-280-217-007||1997-99 All Boxsters||Sensor for use with cable throttle cars|
|996.606.124.00||0-280-218-009||Early 2000 Boxster / Boxster S||Original sensor for E-gas cars|
(thru Boxster 2.7L Chassis #98 6YS 62 0414 and #98 0YU 62 5099)
(thru Boxster S 3.2L Chassis #98 0YS 66 0257 and #98 3YU 66 2413)
|986.606.125.00||Mid 2000-04 Boxster / Boxster S||First updated sensor for E-gas cars|
(discontinued and replaced with version 125.01 below)
|986.606.125.01||0-280-218-055||Mid 2000-04 Boxster / Boxster S||Latest updated sensor|
|987.606.125.00||0-280-218-145||2005- All Boxster / Cayman||Integrated housing design|
If you own a 2000 Boxster or 2000 Boxster S, then you need to make sure that you have the proper sensor installed. Much confusion lies in the fact that most people don't know if their car has been updated by Porsche or not. If the old sensor that you removed is 996.606.124.00, then you need to replace it with the same part number (or have Porsche update your DME software to accommodate the newer style sensor: see Technical Service Bulletin 1/00 2445 Air Flow Sensor -- dated 4-18-00). If the old sensor you're removing ends in 125.00 or 125.01, then replace it with 986.606.125.01 (the latest version available).
After reinstallation, reset your check engine light (CEL), using your code reader (see Pelican Technical Article: Reading Fuel Injection Fault Codes / Diagnosing Problems). You can also disconnect the battery for a short while to reset the lamp, but I don't really recommend this approach (see Pelican Technical Article: Reading Fuel Injection Fault Codes / Diagnosing Problems). On 1997-02 Boxster, you can disconnect the battery for more than 20 seconds, but less than 50 seconds to clear the trouble codes without having to enter your code back into your radio. On pre-2003 cars, the computer's CEL memory is cleared after being disconnected for 20 seconds, but the radio code is needed after 50 seconds disconnected.
After you have replaced or cleaned the sensor and cleared the code, you need to go drive the car and see if the code returns. If the same error code appears, then the problem probably lies elsewhere. Most of the time when you have an error code indicating a problem with the mass air flow sensor, it is usually solved by the installation of a new sensor. However, the computer can become confused sometimes and give misleading error messages. Wire harness issues, DME problems, and secondary air injection equipment problems may all give false MAF error codes. At this point, it's best to dive into the factory manuals and start going through the laborious test procedures contained in there.
Shown here is the mass air flow sensor (MAF). The main sensor fits in a hole in the air intake right downstream of the air filter. The green o-ring seals the sensor to the intake tube (yellow arrow). If you're having trouble with your MAF, you can try to resurrect it by cleaning it. Lightly spray the areas shown with the blue arrow with electrical contact cleaner: the one that I recommend is CRC Mass Air Flow Sensor Cleaner. Spray it and then shake the sensor so that any dirt or debris is washed away. Don't touch any of the sensor elements with anything (like your finger or a brush), as this will damage them almost immediately. Let it dry completely prior to reinstallation.
You need a T20 tamper proof Torx bit (inset upper left and lower left) to remove the mass air flow sensor from its home in the intake pipe (yellow arrow). It's typically easier to pull the sensor out of the intake tube first, and then disconnect the electrical harness. Be sure not to touch any of the sensor elements that are exposed (red arrow). Clean the entire housing area prior to installing your new sensor.