M4 Boost Issues: Power Loss and Check Engine Troubles

Hi there! I've got some experience working on BMWs, though I wouldn't call myself an expert. I had a very similar issue with my 2018 BMW M2. The symptoms were almost identical, check engine light, inconsistent power delivery, and terrible fuel economy. Turned out to be a faulty vacuum switching valve. Had it fixed at my local workshop for about 140 Euro, and the car's been running perfectly since. Before you head to the shop, could you share: Any specific error codes you're getting? Does the issue get worse when the engine is warm? Have you noticed any unusual sounds when accelerating? This might help narrow down if you're dealing with the same problem I had. The good news is, if it is the vacuum switching valve, it's a relatively straightforward fix.

Thanks for sharing your experience with the M2! My M4 actually threw the P0299 code when I scanned it. The power loss definitely gets more noticeable after about 15-20 minutes of driving when the engine is warm. And yeah, there's this subtle whistling noise under acceleration that wasn't there before. I just had my service done at 119,034 KM, and everything was fine then, so this came as a surprise. I'll get it checked out at the shop, but your vacuum switching valve suggestion sounds spot-on given the similarities. Hopefully it's that simple and not something more serious like a damaged turbo. Really appreciate the help! I'll update once I figure out what's causing it.

Hey again! Thanks for providing those details about your M4. The P0299 code and those symptoms, especially that whistling noise, are exactly what I experienced with my M2 before the vacuum switching valve repair. Just wanted to add, after I got mine fixed, I learned these valves often wear out around the 100-120K km mark. And since you mentioned you're just past 119K, that timing fits perfectly. When mine failed, I actually tried driving it for a couple weeks before getting it fixed (not my smartest move), and the fuel consumption got ridiculous, was burning through a tank way faster than usual. Quick tip from my experience, while they're replacing the valve, ask them to check the surrounding hoses too. My mechanic found a slightly cracked vacuum hose during the repair. Apparently, these issues sometimes come as a package deal. Getting both fixed at once saved me another trip to the shop. Hope this helps! Keep us posted on what your mechanic finds. I'm betting you'll be back to full power soon.

I'd reply as: Thanks so much for that additional insight! That's actually really reassuring to hear about the typical failure range being around my mileage. I've already scheduled an appointment for tomorrow morning, definitely not taking chances with it like you did! The fuel consumption alone is painful enough. Really good tip about checking the vacuum hoses too. I'll make sure to mention that to my mechanic. Better to catch any potential issues while they're in there rather than dealing with another problem down the line. And you're right, probably best to get this sorted ASAP before it potentially causes any other issues. Will definitely post an update once I get the diagnosis and repair done. Thanks again for all the helpful information, this community is awesome!