Mass Airflow Sensor: How to test

So being the genius I am and doing a bunch of maybe I'm not a genius. However, we have all read about cleaning MAFs and things like that when they seem to be failing.

On the 2000 VW Passat it is failing, and the other weekend I replaced the plugs and cleaned the mass airflow sensor (MAF). Put it all back together and bam...Check Engine Light (CEL). The CEL was in relation to the MAF not being plugged in all the way. The car still seemed to be lacking so I cleared the CEL and did the little ECU reset with the key in the ignition. Now the car is running great, turbo is spooling just like it should and all the boost is there.

So the other night I popped the hood ready to spend an hour taking apart the airbox. Then I woke up and saw the wires for the MAF running into a rubber stopper. Peeled up the edge and popped off the rubber stopper and needless to say it definitley was not plugged in. So i was able to plug it back in and put the stopper back in place. Voila. The car is still driving great, just not sure for how long.

So you may be thinking, whoopedy doo. Well when your MAF is going you may not be spooling at the right times or even at all, as I was experiencing. So one quick test prior to cleaning or replacing the MAF is to just unplug it. In this instance unplug it and replace the stopper to keep debris and water out of the box. Drive around and see how it feels. If it drives like there's no tomorrow then there is a chance the MAF is bad.

If it still drives like crap then there could be other vaccum or DV related issues. This pertains to the 1.8T on B5s. Keep in mind there are risks in doing it. As always take all proper precautions to ensure safety at speeds and don't run it for a long time especially while boosting. This is just for diagnostic purposes as your MAF does serve a purpose. Also, when you do this you WILL get a CEL and in a 2000 Passat get an alarm with an Emissions Workshop message. The CEL will basically say MAF range too low or something similar because it is unplugged.

On 2000 Audi A6 2.7T it is even easier to get to. I have been having some stumbling at idle when the Climate Control isn't on. And it seems like it takes a long time for the turbos to spool and so forth. So I unplugged the MAF and drove around. The car seemed to accelerate quicker and hold boost longer and definitley put out more boost. When I plugged it back in the stumble seems to have returned and again, seems to be lacking a little.

In the end, this is just one small little diagnostic step. Just remember after plugging the MAF back in you will need to clear the CEL. However, it may clear itself after an unspecified number of ignitions and drive time. The DTC will still be stored in memory though.

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