Badly Dirty Air Filter-- Effects on FE and Smoke?

I feel like an idiot. I got my Jetta just before Thanksgiving, and I've been tinkering on it since. I got a Panzer Plate, PP520 nozzles, new shocks and struts, etc. So this weekend I decided to do as much free maintenance as I could on it. I was going to replace the air filter, clean the snow screen, clean my MAF, etc. With all the work that has been done to this car by me and the guru, evidently none of us had checked the air filter. The stealer put in a new turbo and oil pan to get it saleable, so I just assumed () that things like air filters would have been dealt with. Mine had a K&N sticker on the airbox, so I bought a disposable one to throw in when I got a chance.

I've failed emissions twice, due to smokiness, and I've been getting sub-par mileage. I've been getting very consistent 35-ish MPG in mixed, mostly not-warmed-up commuting. I decided to do a highway MPG test yesterday. Did an errand in Castle Rock and drove down to Trinidad and back at 70-80 MPH, no stops, smooth driving, no big throttle situations. I got a little over 45 MPG over a little over half a tank (360 mi). Filled up at the same pump both times.

I took my AF out last night, and freaked. It is so completely filthy that almost no light will go through it. It has thick black crud on the dirty side, and it's so full of dirt that the clean side is black, too. The seal for the airbox was so buggered up that I couldn't get the airbox shut. I deleted the seal, and I'll get a new one as soon as I can. (I realize that driving it with no seal is a BAD idea...).

So, how much do you think the filthy filter affected my FE and smoke? I'm hoping for a great gain. Anything I should look for that would have been caused by a plugged filter? I'm not seeing a CEL or anything.

I don't know if the filter will do anything for smoke, but I hope you now know that if it says K&N, you don't want it.

Joe_Meehan said:

I don't know if the filter will do anything for smoke, but I hope you now know that if it says K&N, you don't want it.

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Yeah, I bought a regular filter as soon as I saw the K&N sticker. Unfortunately, it took me a month to think to actually open the airbox...

if it was the K&N (couldn't tell from original post), they do collect more crud than a paper filter, plus they're dark in color to begin with. Use a regular OEM type paper filter, try setting your injector quantity higher (for less fueling) or change the timing to reduce smoke. Maybe a diesel purge will help.

The reason I decided early on to chuck the K&N is the only ones I've used were oiled, which doesn't seem like a great idea with the MAF there.

Conan, you are going to need to repair your air box problems and will also need to replace the MAF sensor.

dieseldorf said:

Conan, you are going to need to repair your air box problems and will also need to replace the MAF sensor.

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I tried to clean my MAF last night, and couldn't get it out. I'll try again tonight. Talked to the guru this morning, and he said that a bad MAF would probably cause underfueling, and that certainly doesn't seem to be my case. I'm hoping the fresh filter will help a lot. It does seem to rev a little freer, and be happier in general this morning.