BMW M4 Cold Start Issues: Rough Running & Hard Starting

Hi there! I have some experience working on cars, and I faced a very similar issue with my 2015 BMW M3 last winter. The symptoms you're describing sound exactly like what I went through, rough cold starts and increased fuel consumption. I took it to my trusted workshop, and they diagnosed a faulty fuel injector. One of the injectors wasn't spraying fuel properly, especially during cold starts. Had to replace it, which cost me around 515 Euro, but it fixed the problem completely. The car runs smooth as silk now. What's your mileage, and have you noticed any check engine lights? Also, does it run better once the engine warms up? This could help confirm if we're dealing with the same issue. Just a heads up, since you have a newer M4, you might want to get it checked soon. These injection issues can sometimes lead to bigger problems if left unchecked.

Yeah mine is running well after I got it fixed last month when I faced the same issue. Just got my service done recently at 154927 KM. The problem was actually not just the injector but also the fuel pressure regulator. Had to deal with both and cost me a bit more than what you paid, but it's worth it. Car starts like a dream now. Since it's the same engine family, I'd recommend getting both components checked. Better to fix it now than wait for it to get worse.

Thanks for sharing your experience! It's good to hear you got it sorted. Yeah, you're absolutely right about the fuel pressure regulator, I should've mentioned that in my first reply. After I fixed just the injector on my M3, I actually had to go back about 3 months later because the fuel pressure regulator started acting up too. Ended up replacing both parts eventually, just like you did. These S55 engines are amazing but they can be a bit sensitive with their fuel delivery system. My total bill ended up being around 890 Euro for both repairs combined, but like you said, totally worth it for peace of mind. I'm at 162,000 KM now and haven't had any issues since fixing both components. For anyone else reading this with similar symptoms on their M3/M4, definitely get both the injectors and fuel pressure regulator checked out. Could save you from multiple workshop visits like I had to do!

Hi everyone! Wanted to follow up and thank you all for the helpful insights, especially about checking both the injector and fuel pressure regulator together. My car's been running perfectly since getting both components fixed last month. The workshop also mentioned they're seeing this quite often with our S55 engines around this mileage range. Like mentioned earlier, it cost a bit more than just fixing the injector alone, but it's been a smart investment. No more rough cold starts, normal fuel consumption, and the engine fires up instantly. For anyone facing similar issues with their M4 or M3, definitely worth checking both parts at once, saves time and potentially money in the long run. Really appreciate everyone's input. Nothing beats getting advice from people who've actually dealt with the same problem. Time to enjoy some smooth driving! Cheers!