Found this on the SSOA site:
Today I learned something very important about how to eliminate KR on my LS1. Back in Dec '02 my car Baseline Dyno'ed @ 320rwhp/ 344rwtq (w/out Predator). Downloading the Predator tune, Advancing the Timing 10% & Leaning the A/F Ratio 2.5% brought the total to 334rwhp/356rwtq with 0.00 KR (A/F @ WOT was 12.7:1). Life was good.

But lately I've been getting up to 6* KR above 4K RPM under load with just the Base Predator Performance Tune (0.00* KR w/stock tune). I did the usual stuff, new plugs (needed them anyway), shimmed the T-stat to open @ 178* (instead of the stock 195*), changed my fan1 & 2 settings to come on @ 181* & 186*, and T-body Bypass. The results of all that effort was to change my KR from 6* to 4*. (yea, Whoopi $hi+ ). The only way I could eliminate all KR with the Predator Tune was to decrease the Timing 10% and Richen the A/F by 1%. Something was different.

bullSSeye (on this board) put together a Dyno Day for today at a local shop (ATP in Fremont, Ca), so I signed on so I could check my A/F Ratio on a Wideband O2 capable Dyno, see what's up. With bullSSeye driving and me on the Predator, my neutered timing and fat mixture pulled 326rwhp/344rwtq with the A/F ratio dipping to 11.98:1 @ WOT but 0.00* KR. Next run we set timing to 0* additional (up from -10%) and leaned A/F to -1% ….Ping city (imagine the sound of 2 Skeletons f@*king on a tin roof using a Coors Can for a Condom, that's the sound), but the A/F only rose to 12.3:1 (WTF?) . Then, bullSSeye's friend Scott says "You know, I'll bet your MAF Resistors are coated with oil from that K&N Filter". Hmmm. So I pull out the MAF and after we disassemble it, sure enough 2 of the resistors are Dark Grey . He cleans them with a Q-tip dipped in Alcohol (or was it Brake Cleaner?) and I put it back on the car. Kick the Timing back up to +10%, lean the A/F by 2.5% and Bingo. Almost 335rwhp and NO KR. Problem solved .

Now, I don't over oil my Filter. I normally oil it until it just becomes that uniform "pink" color, then place lint-free wipes in the pleats to soak up any excess oil (I'm **** that way). Still, enough oil migrated onto the MAF Resistors over the last 15,000 miles or so to make the PCM think less air was passing through it, but not enough oil to notice with the stock GM tune.

Anyway, if you guys with K&N or Holley P-shot Filters start seeing KR on your LS1's you may want to disassemble your MAF and CAREFULLY clean those resistors (they look like tiny wire looms) with a Q-tip dipped in Alcohol. From now on I'll be doing this 1 week after cleaning/re-oiling the K&N.

I'd like to thank Scott for teaching me something new (and important) about MAF's , and bullSSeye for handling "throttle duty" during the Dyno runs while I monitored Real Time Data on the Predator plus letting me cut into his Dyno time so we could be sure that we really did solve this problem

And here I just finished cleaning and oiling the filters on the C5

 

Is there a problem with the K&N filter as it comes from the manufacturer or did the problem arise from you putting too much oil on the filter?
I have never re-oiled my filter-do I have, potentially, the problem you are talking about? :confused:

 

You may after you clean the filters with K&N cleaner then oil them with the K&N spray oil. Like he says, give it about a week or two and clean the MAF. You should be ok after that. If you haven't cleaned and oiled your K&N's since you purchased them, you might want to give it a try.
:flag

 

Donaldson has a kit to clean and oil the filter. The filtering media is dependent on the oil - don't run your car with a dry filter, because you won't be filtering much if anything !! I've heard you can use mineral oil too, but for the small cost of the kit (approx. $15), why chance it ? I've also heard do not use K&N oil, as the filtering media are totally different.