BMW M4 Cold Starts Draining Fuel, PTC Heater Alert

I had similar issues with my 2016 BMW M3. The symptoms you're describing match exactly what I experienced last month, sluggish warm-up, rough idle on cold starts, and terrible fuel economy. Took it to the garage and turned out the electric auxiliary heater (PTC) was completely dead. The mechanic found that the heater element had failed, causing the system to malfunction. They had to replace the entire PTC heater assembly and reset the control module. It was a fairly serious issue since it affects engine performance and emissions. The repair took about 4-5 hours, and they had to order specific parts. The rough running during cold starts was because the engine was compensating for the failed heater by adjusting the fuel mixture. The car runs perfectly now, quick warm-up times, smooth cold starts, and fuel consumption is back to normal. Don't wait too long to get it checked out, as continuing to run with a faulty PTC heater can potentially cause other issues.

Thanks for sharing your experience! That's super helpful as it sounds exactly like what I'm dealing with. Really good to know it was actually the PTC heater in your case. Would you mind letting me know roughly what you ended up paying for the whole repair job? Also, has everything been running smoothly since the fix, or have you noticed any other quirks?

Hey again! I'm happy to update you, after getting the PTC heater fixed, everything's been running like a dream. The repair bill came to 350€ for everything, including parts and labor. I know that's not cheap, but considering how much better the car runs now, it was totally worth it. It's been a few weeks since the repair, and I couldn't be happier with how my M3 is performing. The cold starts are buttery smooth now, warm-up time is back to normal, and my fuel economy has improved significantly. No more watching the fuel gauge drop like a rock! Really glad I got it sorted when I did. If you're experiencing the same symptoms, I'd definitely recommend getting it checked out. The whole repair process was pretty straightforward once they diagnosed the issue, just needed to replace that faulty electric auxiliary heater. Haven't noticed any other issues since the fix, and the car feels just like it did when it was new. Trust me, you'll notice the difference immediately after getting it fixed. The engine performance is so much better when all systems are working as they should.

Thanks for the detailed follow-up! I took the plunge and got my M4 checked out at a new mechanic I found. Turns out you were spot on, it was indeed the PTC heater. The repair cost me a bit more, around 450€, but what a difference it's made! Just had my first proper drive since getting it back, and it's like driving a completely different car. The cold starts are perfect now, and I'm not burning through fuel like crazy anymore. The engine warms up so much quicker too. Really glad I didn't put off getting it fixed any longer. The mechanic was actually great, showed me the old part and explained everything. Much better experience than my last garage. Thanks again for sharing your story, it gave me the confidence to get it sorted. I guess sometimes you just need to hear from someone who's been through the same thing!