Dirty air filter/mass air flow sensor



I am so disgusted with myself for taking my mechanics word on something; never again. 7k miles ago I had my 60k maintenance done at the Mazda dealership (I drive a '03 MazdaSpeed Protege). My car has an aftermarket (Injen) cold air intake with the filter placed in the driver’s side fender just in front of the wheel; the only way to access it is from underneath the car. When I had my 60k done I made sure to pointedly ask several times about the air filter; I wanted to be sure that the dealership had cleaned or replaced it (it’s like a K&N filter). They insured me that they had properly cleaned it and that it looked fine.

LIARS!!! After my CEL came on with a P0171 code I posted another post on Car Talk asking you folks what course of action to take, and I was told to replace the K&N style filter with a regular air filter and clean the mass air flow sensor and see if that helps. Well I replaced the air filter and upon pulling my old filter off it was OBVIOUS to me, and anyone else, that that filter had WAY more than 7k worth of dirt in it; probably more like 20-30k worth of gunk. I’ve had this car for about 10k miles.

I want to take that old filter down to my dealership and raise some hell because I was pointedly LIED to. When they lied to me I had asked them to describe their methods for cleaning the filter and I thought I had pinned them down on it as I was very concerned about this being done properly. This will be the last time I ever take anyones word on something that involves my investment/baby. Do you think I have any recourse? Can I demand that they replace my O2 sensor if it needs replaced? That was a simple step in the repairs they were doing and I can’t believe that they didn’t do it because we all know how important it is to have a clean air filter on your car.

Also, I bought some MAF cleaner and was going to clean it but I want to make sure I do it right. I found what I believe is the MAF on the intake tube between the filter and the engine. I tried to use a screw driver to remove the lid on it and it’s not coming off. I didn’t want to force it. I already broke two of the four snaps just trying to open it and I don’t want to cause more damage. I am sure that it needs cleaned sinced the air filter was neglected for so long. Any suggestions? Do I even have the right box?


Anyone that puts that junk on a vehicle shouldn’t take it to a dealer. The dealer did nothing to damage your vehicle and they definitely do not owe you an O2 sensor. Learn to fix your own vehicle!


Wow, that’s rough!!! Not very nice, but thanks for the reply anyway. I did not put the intake on the car. It was like that when I bought it 8 months ago. If the dealership had simply said that they would not perform that service and that I needed to take care of it myself that would have been fine, but the point is that they LIED to me and said they did do it. Trust me, I will be taking care of it myself from now on. I am not a complete car idiot, but I am still learning about “rice burners” as all my previous experience is with old Chevy’s with V8’s. Anybody know any websites that sell shop manuals?


He’s rough but honest and true. First off WHY use one of those Junk filters in the first place? The dealership is NOT going to service that kind of filter. They know their vehicles and the parts it came with. Get rid of the K&N filter and replace with OEM or equivalent paper filter. You’ll be far better off in the long run.


So I went down to the local motorsports shop and talked to them and they explained to me that I would have to disconnect the intake tube because the mass air flow sensor is actually inside the tube where they are joined together. So I’m on it!! I’ll pull that off and clean the wires in there with MAF cleaner.

I also learned today that there are socks that you can buy to put over the air filter that prevent water from getting in when you have a cold air intake with the filter close to the ground. Apparently these socks are 99.9% permeable for air and not at all for water. I might give that a shot because I don’t want to run the risk of hydro-lock. Does anyone know if these things work?


I would like to get a paper filter for my car, but I can’t find one for this particular application. All the autoparts stores are telling me that I have to run an oiled filter on cold air intake. I spent all day looking at all the stores in town and nobody carries paper filters of this type.


The car came STOCK with this setup??? If so that’s the first car I’ve ever heard of that came stock with a K&N filter. If it didn’t, then go back to stock.


What are the chances of the person you bought the car from to still have the stock air cleaner parts? Maybe in long run you might be better off putting the stock setup back on.


There is no reason why you can’t continue to use the K&N. Just be aware that people have a tendency to over oil them. Microscopic particles of oil over time coat the airflow sensor. If this is a hot wire type, that oil collects dust on the wire and thermally insulates it. That throws the airflow calibration off. When you see modified airflow systems on vehicles it is a good bet they have been driven hard. Your codes may reflect that


I agree, best is to put it back to stock.

Or heres another possibility: See this link, they might have an oil less replacement element for your cold air intake.

Check helminc.com for the shop manual & i’ve found on my Fords that the factory electrical troubleshooting manuals with their excellent wiring diagrams are also worth their weight in gold for solving electrical problems.

I’ve been surprised by the number of electrical problems i’ve been able to solve by simply understanding how a circuit works.

The way to understand how a circuit works is by looking at a GOOD set of wiring diagrams.


It’s not stock. I bought the car used like this from a dealership.


Then I suggest you go back to stock.