dat280zz

Seeing that the K&N air filter and stock GM air filter are both around $95 I put in the K&N. A few weeks and about 100 miles later the check engine light came on when I started it up. At the same time the idle was a little rough and fluctuated about 50-100 RPM. I Took it to a Chevy dealer and the fault code was P0171 and P0174, fuel trim lean left and right banks. For the next 3 days they were trying to find the problem. Vacuum leak test OK, fuel analysis OK it contained 11% alcohol, nitrogen and smoke test of intake system OK, cleaned fuel injectors, fuel pressure readings OK, reset oxygen sensors, fuel trims running 20-24 per bank (which I think is lean).

After I was reading up on the problem in the internet I saw where a K&N air filter could shed some oil and damage the mass airflow sensor so I told the dealer to replace it and had enough of their troubleshooting so if the sensor fixed or didn't fix it I was picking up the car. They replaced it, reset the codes but the light came back on.

After getting it home I was checking the internet for any more ideas and ran across this site where someone was reporting a similar problem, took out the K&N air filter and installed a GM filter and everything then worked OK.

I also removed the K&N air filter and reinstalled the slightly dirty old GM filter, reset the light by disconnecting the battery, started it up and no check engine light, drove it around and all seems OK now including the idle. I have no idea why an air filter can cause a problem like this.

This site has a lot of good info and I'm sure I'll be using it again, so I just wanted to give everyone here an FYI in case you run into a similar problem.

gsflyer2011

Yep, you should have researched K&N filters here on the forum before you wasted your money on one. I had the same experience 4 years ago but I was able to narrow it down to the filter without taking it into a dealer. I sold it here on the forum for 50 bucks and posted a thread on it. Some smart a's laughed at me at that time, but than lot more posts came out like that after the fact. Apperantly there are some people here run K&N filters here without problems, but on a vette it is a problem looking for a solution. The stock filter is the best, it flows more air that you need and also keeps it clean the best.

Internets_Ninja

On modern cars you cannot change the airflow characteristics which will affect the MAF's ability to accurately measure the incoming air. Most will throw codes. It's easy to tune for it if you have HP tuners but thats a $600 investment. My advice would be if you don't plan on modding the car at all then stick with everything bone stock, including the paper air filter.

Nooch8it

I had the same exact problem on my 2011 grand sport. Gm dealer techs are idiots half the time and don't have the skills needed to find the issue. You need to check/watch your fuel pressure. Mine was slowly dropping causing the ecu to correct until it could no longer keep up. My issue was the fuel pump and fuel filter. My fuel pressure dropped from 58-60psi to 35-40psi at idle. Good luck

long_tall_texan

There is a less expensive alternative than HP tuners, or any local dyno tune. You can buy a used DiabloSport Predator on eBay or craiglist pretty inexpensively. I got one local on craigslist for $40. Then have Lew at DiabLewTune.com do a custome tune. Much less expensive, and his tune fixed that exact problem for me with my K&N whole intake system combined with Vette-Air scoop and Beehive.

C5 Hardtop

This problem has been around since K&N released those filters. People swear by them. Like others have said, paper is the way to go. Wix is my favorite brand.

The issue you may have had was from too much oil. The #1 problem of using those filters. Its hard to oil them correctly w/out training. Even then, why take the risk for such little gain.

The air spreads oil off the filter and into the sensor. Have you inspected the MAF while its off the car? Hold it up to the light and see if oil is anywhere around there.

The K&N filter without oil is not going to cause these problems. I've seen people put panty hose over the intake at the drag races w/out problems as well as running without any filter and all. What that does is gives the engine more air, but at the risk of ingesting something that could damage the engine.

Internets_Ninja

True this is also an option. I tune my own cars so I didn't think of this option.