I replaced the stock air filter in my '05 X with K&N's high performance drop in replacement replacement filter. Now my truck feels "off". The engine feels a bit sluggish at lower rps, and then gets a sudden surge of power when accelerating...almost like a turbocharged engine does. Is this behavior to be expected? I figured the oxygen sensors would automatically detect increased O2 levels and the ECU would adjust fuel flow accordingly. Would disconnecting the battery overnight to let the ECU reset itself have any effect on the fuel flow? Perhaps changing the way it interprets data from the throttle sensor? Or would this make no difference at all? Thanks.

A more knowledgable member probably should confirm this, but I believe I yes.

As I understand, there are computer variables that are set and determined over a period of time that the computer takes for granted on ignition. While over time, it will adjust these variables itself, reseting the ECU should speed up the process.

Noobie001

Sometimes when first replaced the air box does not seal well... I know that may sound dumb but I'd start there. I'm actually surprised K&N has one already... it took awhile for the Titan when it came out.

I still have the lingering thought in the back of my mind that there is a slight chance mine isn't completely sealed even though as best I can tell it is.

Noobie001

To check the seal, you can hit it with some test spray and see if its drawn in...and the ECU has to re-learn the curves, so there is a time lag before it can run right again.

And make sure the intake hose is on tight, mine came off once and I had the same symptoms. It eventually came all the way off and the engine kept dying. It all went back to there not being enough air flowing through the MAF sensor.

See the other thread here re Mass Air Flow Sensor and aftermarket filters.

Samething happenned to me too. The last thing I had done before this problem was to put a K&N drop-in so I openned the hood to remove it when I noticed the hose disconnected.

I don't get it. Everything is sealed tight, as far as I can tell. I disconnected the battery to clear the ECU. The truck seamed to drive better right after that, but seems to have gotten worse over time. Acceleration just feels a bit sluggish. Merging on to the highway last night, I floored it and could have counted the seconds it took to get from 40 to 60...lots of noise, but no feeling of power. The truck actually seemed to perform better with the stock air filter installed. I'm sorry I didn't time the acceleration for comparison. I think I'm going to buy another stock air filter (threw the old one out) and compare them empirically.

Keep us info'd on the results... at least I'd like to know!

If anything, it's good to have a paper filter handy to put in when you clean the other one, that way it gives time to let it dry properly.