Just posting this in case anyone had or is currently going through the same issue... I got a 525i for dirt cheap with the engine light on, fixed a few things in it but it stayed on. It started “acting up” and stalling or losing power while driving which became very dangerous. Getting it scanned at auto zone showed a lot on lean codes and pointed towards a MAF which I then cleaned the first one, no change. Then replaced with a new one and new filter, no change. I checked every hose and O ring I could to see if there were any torn parts or corrosion but found nothing. Car went into limp mode or transmission fail safe mode and was stuck and limited to 3 gear. I dug around around searched some videos to realize that the disa valve was bad and caused the source of everything, even though the scanner said it was a bad MAF. Luckily didn’t spend too much on parts and didn’t buy things I wasn’t gonna need. It only takes a couple minutes to check the quality of the o rings and pressure system of the valve if you have a “mystery” vacuum leak. Changed it and the engine light is gone!
The first thing that needs to be done is to have the intake smoke tested with a professional smoke machine. There are an infinite number of places (ok, almost) where the intake can develop vacuum leaks. Visual inspects will find the large cracks but not the leaks buried under the hoses and wires. Find a reputable indie shop that specializes in bimmers at www.bimrs.org.
The shop needs to have all the proprietary BMW software and a professional smoke machine. The shop needs to scan the engine computer (DME in BMWspeak) and the automatic transmission computer (EGS) for codes and data.
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