Pelican Technical Article: Troubleshooting and Replacing the Mass Air Flow Sensor (MAF) Wayne R. Dempsey
Time: 1 hr
Tab: $300
Talent:
Tools:
Tamper-proof T20 Torx driver
Applicable Models:
986 Boxster (1997-04) 987 Boxster (2005-08)
Parts Required:
Mass air flow sensor (MAF)
Hot Tip:
Try cleaning the unit first.
Performance Gain:
Smoother running engine
Complementary Modification:
Replace air filter.
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.
Check out some other sample projects from the book:
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:
(thru Boxster S 3.2L Chassis #98 0YS 66 0257 and #98 3YU 66 2413)
996.606.125.00
0-261-231-148
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.
Figure 1
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.
Comments: I got the CEL light and a local Porsche specialty shop diagnosed and replaced the MAF sensor. The car now runs smoother but has much less jump and power than it previously had. Further, it has a much quieter sound. My fast fun car has become a slugish cruiser. The shop suggests this is normal. In your opinion is this typical of a MAF change and if not what do you suggest has happenned and what should I do?
May 14, 2013
Followup from the Pelican Staff: Replacing the MAF sensor should restore lost performance, not necessarily degrade it. Have them check the vehicle and see if everything is installed correctly and no fault codes are stored. - Nick at Pelican Parts
Upnorth
Comments: Guys, no need to go and buy a T20 tamper proof torx bit ... Just take a 1/16 drill and "create" your own. Piece of cake
April 20, 2013
Followup from the Pelican Staff: Great tip. Thank You!
Craigieboy1
Comments: Help! Just had new stage 1 exhaust, ipd plenum and 74mm tb installed along with cold air intake. As part of work, aos was replaced and water pump. She's now idling badly and running worse. Improves when I remove maf or if I take off oil cap. You can hear hissing and feel vacuum when removing the oil cap or dipstick, but it wasn't hard to remove so I'm guessing that points to a crankcase leak somewhere?
March 15, 2013
Followup from the Pelican Staff: You'll want to double check AOS connections. Keep in ind, removing the oil cap will create a vacuum leak and change the way the engine runs. Are there any fault codes stored? - Nick at Pelican Parts
Paige
Comments: I'm trying to figure out the type of MAF I need for my 2000 Porsche Boxster it has the smaller engine.. My vin is 2987YU624042 and it doesn't match up with any MAFs here. Which one would be right for my car?
November 26, 2012
Followup from the Pelican Staff: Give our parts specialists a call: 1-888-280-7799 They will help you find the right MAF sensor. - Nick at Pelican Parts
Kaan Celebi
Comments: Good morning, I am about to purchase a MAF for my 2001 Boxster, I believe the part number is 986.606.125.01. The VIN is WP0CA29801U623269. Could you confirm before I order it online? Thank you, Kaan.
November 6, 2012
Followup from the Pelican Staff: Give our parts specialists a call: 1-888-280-7799 They will help you find the right MAF sensor. - Nick at Pelican Parts
Osio
Comments: After detailing my 2000 Porsche boxster started it and for a moment it ran ruf no CEL light on but it would not rev over 1800 RPM The shop changed the throttle body.After clearing the code 1502 it went in to limp mode again.After that they said it needs a new ECU.After that I payed the bill of $1095 and took the car home Still trying to learn something about this problem.I would greatly appreciate if someone could possibly help me with this headache.Regards Osio
September 6, 2012
designprof
Comments: I have a 1999 Boxster that was giving me P1124 and P1126 codes. I replaced my MAF, and reset the cel by disconnecting the battery for about 1 minute. All was great and the car ran well. Next day rough start - coughing and not able to idle. Reset cel again and all is great. Next day, same thing! Why is the ecu not adapting to the new maf? What am I doing wrong?
September 5, 2012
rodgers
Comments: i changed mafs on nissan altima runs fine but it jerks some when i go 45 does it reboost itself in time cuz no codes on or engine light not on
August 28, 2012
Followup from the Pelican Staff: You may have an engine misfire. I would look into that possibility. - Nick at Pelican Parts
Brian
Comments: I have all the signs of MAF issue. check engine light with applicable codes. But just yesterday, it started roughly and then would only idle. Nothing would happen when I pressed the gas pedal. No acceleration or engine rev at all. I turned off and on the car a bunch of times before it finally worked. Could this be part of the same issue. If not. Any other ideas!? It's a 2000 boxster s.
Thanks. Brian
June 4, 2012
JDUB
Comments: I have a 2011 Cayman S. Do you offer a replacement MAF sensor for this version of the car?
May 11, 2012
Followup from the Pelican Staff: We sure do - you can check our catalog, or give our sales guys a call at 1-888-280-7799. Thanks! - Wayne at Pelican Parts
JJ
Comments: The maf sensor installed currently on my car that needs to be replaced has this part number- 996.606.125.00. Which maf should I order? Should I go with the 986.606.125.01 as advised by this article? The vin on my 2001 Boxster S is WPOZZZ98Z1U640725. My engine number is M96/2167102466. I'm just making sure because I was told that most electronic parts, such as MAF are not returnable.
March 17, 2012
Followup from the Pelican Staff: Yes, the correct (and only available version for your car) is the latest version of the updated one - 986.606.125.01- Wayne at Pelican Parts
Stan
Comments: I have a 99 boxster. Last week driving home from church my lil b started idling all funny. idle would just fly up and down between 1400 and around 2000 rpm. Reading up on forums i was pretty sure it was the maf as when i unplug car runs fine and dont miss a beat. Pluging it back it in it goes back to the same problem. I replaced the maf sensor with one from buy-auto parts.com and when i plug it up same problem. Buy auto parts offers 1 year of warranty and is an authorized bosch seller. What did i do wrong? I do have techart intakes with k and n if that helps. As well as tpc supercharger kit with other bolt ons.
February 13, 2012
roanokebarry
Comments: I wish I had read this blog before having my maf replaced cost me over 700 bucks....
January 8, 2012
Followup from the Pelican Staff: Thanks for the feedback on the article. - Nick at Pelican Parts
Jwplumber
Comments: I replaced the stock air filter on my 2001 boxster with a k&n two days later the engine light came on. I am told that this is commen due to the amount of oil the company puts on the filter interacting with the mass airflow sensor. I used the suggested cleaner and so far it is off. Thanks this site is great it has always helped me with repairs on my Porsche .
September 24, 2011
Followup from the Pelican Staff: Yup, I'm not a huge fan of "reusable" filters, as I don't believe that they filter as well as the stock units. I have one of these on my own Boxster, but that's because we have a special cold-air intake system that we had to install when we put in the 3.4 engine. - Wayne at Pelican Parts
Croman
Comments: I purchased a 2000 boxster last year and soon after the cel light came on. I took it to the local Porsche dealer and they said the mass air flow sensor needed replacement. They did so as well as checking out the car in general. Before the light came on the car ran rough at times. This year I am having the same problem - running rough when accelerating. I removed the MAF and it appears to be very clean. The number on it is 996.606.124.00 I never saw the one they took out. My boxster was dated 07/99 and the vin is WPOCA2983YU620148 - looking at my gas pedal it looks like a cable comes from the unit. My question is do I replace the MAF and if so which one?
PS...Just took a 20 minute drive w/o MAF connected and it ran great and didn't miss a beat.
June 15, 2011
Followup from the Pelican Staff: Yes, it would appear to be a fault with the MAF, particularly if you unplug it and it works fine after that. I'm not sure what the dealer did - I would buy one from Pelican and replace it yourself. Also, if you have a K&N style air filter that uses oil and doesn't filter as well as the OEM unit, then you might experience this as well. - Wayne at Pelican Parts
keith sp1
Comments: recently changed the maf on my boxster s by following your superb instructions,saved some money by doing so to.great job guys many thanks.
April 24, 2011
Followup from the Pelican Staff: No sweat! - Wayne at Pelican Parts
Joe D
Comments: I recently Installed a softronic Flash and racing plenum in my 2006 boxter non-S version. The car have been running great. But since the installation my check engine light has come on 3 Seperate Times. The flash and plenum were installed by my Porsche Dealer. So far they have not been able to figure out whats causing the issue. Installation has been checked and a re-installation was done, problem still exists. we are now trying a replacement of the sensor. Has this scenario happened with other similiar installations and are we going in the right direction
March 16, 2011
Followup from the Pelican Staff: Yes, these types of issues are common with flash upgrades and non-stock modifications (unfortunately). I would contact Scott Slauson at SoftTronic and perhaps he can assist you with debugging the problem. - Wayne at Pelican Parts
boxsterg
Comments: I recently purchased a 2000 boxster with cel light on. I've cleaned the maf, replaced the air filter, checked for any leaks etc. Code reader says maf. My chassis is 4yu623351 my current I'm assuming not stock maf only says PBT-GF-30 which sensor do I need.
March 3, 2011
Followup from the Pelican Staff: There should be a BOSCH part number on the sensor itself, you should be able to see it there on the side. Your chassis number is not familiar to me, can you post the full VIN on the forums and I will check the PN with the Porsche parts diagrams. - Wayne at Pelican Parts
Will
Comments: I did exactly as this article said and cleaned my MAF and everything worked perfect! Thanks for everything!
November 9, 2010
Followup from the Pelican Staff: Cool deal, glad it worked out for you! - Wayne at Pelican Parts
Check out some other sample projects from the book:
