Check Engine soon light on

About every two to three weeks my check engine light comes on. When checking it is always three cylinders are running lean. I do not notice any difference on the way the car drives or sounds. Every sensor has been changed. What could be causing this????????

I am surprised your not getting both banks throwing the code. How many miles do you have? I had this same problem with my car and the only way I finally got rid of them was replacing the CCV. I also did the valve cover at the same time. I am not sure if that really had anything to do with it.

Did you test your fuel pressure? It could possibly be a sign of a fuel pump or regulator going bad? Perhaps a bad new o2? Did you check all of the vacuum lines?

The Car has just under 112000 miles. Vacuum lines all ok. I will check fuel pressure. Thanks

Maybe something like clogging fuel injectors? Do you run any cleaner? Have you ever had a fuel system cleaning? Just trying to bounce ideas off he wall at this point. Any luck figuring it out?

Yes I do use Cleaner. I just switched gas from Shell to BP. the car seems to run better on BP Millage is up slightly. It contains less alcohol than Shell.

There might also be a cracked intake boot. Hard to find; try using smoke or other methods.

Yep I forgot to mention that. The lower intake boot will form cracks in the inside of bend by the other hose inlet. It is very hard to see unless you remove it and flex it. This is a pretty common issue on a e46. Fairly Inexpensive part. You will have to remove the air box and maf to get to it. You shouldn't have to remove it from the throttle body to flex it enough to see the cracks. Most dealers stock this part.

I will check. Thanks

I thought about this a little bit more. There might be a small chance that the DISA valve might be broken or damaged.

Update Now that I have used about 6 tankfuls of BP gas,and a bottle of Gumout the Car is running great.
I was using Shell V power Car seems to run better on BP.
Bluewagon

Update #2 Feb. 12 light is still off.
When valve cover gasket was changed a new set of plugs were put in. Another bottle of gumout used.
The car is now running better than when I purchased it.
bluewagon

I am happy for you. I am not so lucky. My issue seems very much worse.

Maby a coat of Wet Paint would help..
Just kidding.
bluewagon

I told you I would try it! Just drop a bottle in the mail!

FYI for future searchers, the most common causes of "Bank 1/2 lean" errors are:

- Air leaks in the intake, even as simple as a poorly seated airbox/filter seal (been there), as mentioned the intake boots are prone to heat degradation and cracking around 100k mi (varies with climate)
- Need to run fuel system cleaner (Techron recommended), like you did, run two back to back treatments, primarily to provide better combustion and remove debris from the pre-cat O2 sensors
- Cracked CCV seperator (under intake)

If only one bank lean (1 or 2) is indicated:

- Priority to the fuel treatment (easier possible fix)
- Possible intake manifold leak on a specific intake runner or intake runner to head mating surface, thus effecting only part of the sensing system
- Possible O2 sensor failure

It is now the 20th of June light is still off. The two bottles of Techron back to back seemed to work. Along with a switch in gas from V-Power to B.P. I believe B.P. has less Alcohol.
bluewagon