My car is throwing a Left and Right bank lean code (CEL). I have reset it and it came back on again after a few hours.

I have a Renntech stage 2 tune.

Anyone else running lean after installing after market air filters???

There have been a few people that experienced this. I believe the fix is making sure the box tops are on even and tight and the rubber hoses are snuggly on the box tops. I am assuming the MAFs are plug into the connector?

What happens when you put the stock filter and charcoal back on?

I would love to get some feedback too, below is the text from my post.

No, you are not dreaming. I also had that same issue with just K&N filters and the charcoals removed. I was getting lean codes as well and it happened several times.
I put the stock filters and I had the dealer reseting the CEL when I took it for service A.
It is not about the oil in the filters, it is about the flow going through and the AFRs.

Do you feel any gain with K&N?

I never "felt" any gain with a Renntech airbox and K&N filters however consistent back to back pulls on a dyno indicated a 5-6 rwhp/tq gain so....

I take it you are running stock filters again? I am going to try k&n's with charcoal's.

I had the same issues when I removed charcoals and put K&Ns in. Car threw codes (running lean) and actually once in a while hesitated. Ended up putting stock filters back in (still charcoal removed) and car ran great without issues for 10000miles.
Just got my Eurocharged tune and thaught I would try to put K&Ns back in.
So far no issues (only 1 week on car though), I guess the tune is helping here.

I would have thought you would have felt something. The Renntech box looks to be the best out there with those revised and smoother runners.

Just 5rwhp gain on 450rwhp+ would be hardly feeled with bud dyno. That gain might be from Renntech airbox than k&n. Thanks.

Another thing I think the lean from K&N might not be from flowing lot more air. Engine with OBD II could adjust/compensate to -+10%.
This is what I think. Oil from k&n might get/evaporate in mass air flow(Maf). Maf now reads lower value cause it is lightly coated. ECU cuts fuel little accordingly. Now your engine is running lean. (cause same amount of air going in but Maf thinks it is less.)
If you have scanner, check if LTFT(long term fuel trim) at idle is + more than 10%.

It's not the filters; it's almost certainly some sort of leak when you put the air boxes back together. I had this issue just after I installed my BMC air filters (and had my charcoals removed previously with no issues). I took it to RENNtech, but they couldn't find the leak. So, I took it to my dealer, and guess what? I had a crack and a leak in the air intake manifold...they replaced it under warranty and I said goodbye to the "lean" codes.

Yes, that is the case(running stock air filters again). Keep in mind a few things though:
1)I am driving at altitude
2)I am running 91 oct
3) I am running with very high temps
4)I am running in a very dusty area

All those 4 factors contribute for the car to run "weak". I have had the stock filter now for about 550 miles and no issues so far. My gas mileage got significantly worse though. The K&N filters for sure gave me better gas mileage.

I have the K&N's and also had the CEL's afterward.. This may have already been said but you have to clean the mass air flow sensors. I used a small amount of carborator cleaner and the CEL's when away.. You will have to pull the mass air flow sensors out of the housing to clean them properly.

How do you work those clips off? If you buy the ROW airbox tops, you get another set of MAFs. Too bad they don't sell the box top w/o the MAFs to reduce cost.

If you choose to clean MAFS use a cleaner that is a) plastic-safe and b) leaves no residue. Most cleaners are a) not and b) leave a residue.

http://www.amazon.com/CRC-05110-Mass.../dp/B000J19XSA

I took the KN filters out and put the stock ones back in. Code is gone now.

I inspected the intake, there was no leaks to be found.

Took the MAFS out on each side, both were very cleaned, looked brand new so I left them alone.

My 2007 CLS63 started to throw left bank lean code right after the removal of the charcoal filters and installation of K&N filters. But why the lean code on the left bank only and the right bank seems OK. Need the code gone for a E-test in Ontario, and really don't want to put the stock ones back in.
Brian

I don't think you have any other choice except to reinstall the OEM filters. You can switch back after. Sometimes if you drive enough the ECU may adapt the trims back into an acceptable range for the ECU but chances are iffy at best. If you want to run without lean codes you will likely need to run the OEM filters. The MAF scaling seems to be too sensitive to the airflow to run higher flowing filters in the M156 cars before 2010 MY.

Does removing the charcoal filters really make a difference?

Removing the charcoal filters and installing AFE's with ROW boxes made a noticeable difference. Anything that you can do to increase airflow will result in more hp/tq.

I just put ROW boxes on. No codes and after a week of driving, it feels a bit more "willing" when I get into the throttle.

Now, it took a week to notice this feel and there were a few unusual hard downshifts at stops but that cleared up. Am I wrong thinking the computer needed time to figure out the new configuration and MAF sensors?

TC

My car took about a day to adjust and then it livened things up a bit. I noticed more throttle response more crackling and pops and even a more aggressive cold start. I have the V6 tune and I think the ROW boxes work well with it. I have heard that the ecu needs to "learn" to adjust when you make changes.

Hi there, I just got the same problem. Just wondering if you have the problem solved yet? When you say you put the stock filter back, do you mean just the paper filters or also the charcoal filters? Really wanna get rid of the CEL. Please let me know. Thank you!