Hi i put a k&n a air intake with a universal air mass flow sensor tube to connect the intake to the filter i have the ck engine light on ever since i cleaned the sensor with maf sensor cleaner i thru away all the old airbox i dont know if it on backwards there an arrow on the top of the sensor is it to point fron or back? and is that going to fix my check engine light problem code is p0175 and p0172

 

Try the flow sensor in the other direction and see. The arrow usually means to install in the direction of the air flow, i.e. towards the engine air manifold.

 

Oiled filters and MAF are not happy partners due to contamination of the hot film sensor element. And changing intake piping and filters on a 525 won't make a noticeable difference in performance unless it's a bit more noise. For my money, clean the sensor and put it all back to stock.

 

I agree, but OP has said that he/she threw away the original air box.

 

Auto wrecker.

 

I have a 04 525i and I'm wondering if anyone knows how many air filters are supposed to be in the stock air box? I open mine up an noticed the filter was a red k an n so I bought the cleaning kit an cleaned the filter I had but one day at the junk yard I was looking a a 530 or 535i an inside of his air box he had two filters, the lower one that just sits inside the box, which mine has, but the top filter my car does not have, the filter is connected to the inside of the air box lid an is definantly not as easily removed as the lower filter is, both cars have an identical air box other than the top filter that I don't have, looking inside of my air box I cannot tell if I'm supposed to have the upper filter as well or if that is for another model but from what I can tell it would fit inside. does anyone know anything about this issue?

 

You can look up your filter system on Real OEM. But your best way forward it to take that K&N filter and throw it in the garbage. Put in a new OE style Mann, Hengst, Mahle paper filter in its place and drive your car. Oiled air filters may be a performance improvement on some vehicles, but BMW OE filters have so much surface area that they flow just as well as oiled gauze filters, and keep flowing well when they get loaded with dust. Oiled filters are usually over-oiled when cleaned and that's a recipe for issue with contaminated MAF. Chuck it.

 

But one needn't keep the charcoal filter. It was installed to collect the back fuel fumes from the engine when the engine is shut off and not permit them to enter the atmosphere. Its a very small pressure drop through the charcoal filter, but what the heck. After market filters and so called "cold boxes" are worthless and possibly damaging.

 

so could that be why I hear a gasping sound real quick when I turn off the engine?