Fuel Trim Bank Codes

[glassjoe]

2004 E53 X5 3.0, 117K miles

Hello, all. I recently had my Service Engine Soon (SES) light come on and instead of going to Autozone for a read, I recently bought a cheap OBDII reader (Creator C310 BMW Multisystem Scan Tool) on Amazon to see what codes it was throwing. They are:

E4 Fuel Trim Bank 2, Permissible Range Exceeded
E3 Fuel Trim Bank 1, Permissible Range Exceeded

I'm relatively mechanically inclined and would like to try and resolve this myself without going to a shop. I bought this '04 X5 with 106K on it and it now has 117K miles on it and has run well to this point (besides an oil pan gasket I had to have replaced). Upon start, it runs a little rough at idle but smooths out when I'm driving. I've cleared the codes and within 1 drive to work the light comes back on and the codes are the same.

I did some Google searches and didn't really find a smoking gun on what these codes are indicating is specifically wrong. I have cleaned the MAF with cleaner but that didn't do anything. I've read where it can be O2 sensors, the DISA, vacuum leaks, etc., but what I was hoping to find is a methodical approach to resolving the issues instead of throwing parts at it in an attempt to see what works. My son has a 2002 E53 so I thought about swapping the MAFs to see if that makes any difference.

If anyone has any suggestions on a systematic approach to take in trying to resolve this issue it would be greatly appreciated! Thx