BMW 3 Series Rough Idle & Stalling: IAC Valve Crisis

I had almost identical issues with my 2016 BMW 4 series last month. The symptoms you're describing match exactly what I experienced, rough idle, stalling, and inconsistent RPMs. Took it to my garage and turns out it wasn't the idle control valve. The intake manifold was heavily contaminated with carbon deposits, which was causing irregular air flow. The mechanic showed me the buildup, it was pretty severe. They had to do a complete intake cleaning and remove all the carbon deposits. After the cleaning, the engine runs smooth again, no more stalling or rough idle issues. For a BMW, this is actually a common problem that needs attention, especially at higher mileages. Not a cheap fix but definitely something you want to address before it causes more serious engine problems. The cleaning service was pretty extensive and took about a day to complete, but worth every penny considering how much better the car runs now.

Thanks for sharing your experience! This definitely sounds like what I'm dealing with. The carbon buildup explanation makes a lot of sense, especially given the mileage. Would you mind telling me roughly how much you ended up paying for the cleaning service? Also, just curious, have you noticed any other issues pop up since getting it fixed?

Hey again! Happy to give you an update. So after I got it fixed (cost me 425 € for the whole job), the car's running like a dream. The mechanic actually found it was both issues, the idle air control valve needed fixing AND there was that nasty carbon buildup I mentioned before. They did a thorough intake cleaning and sorted everything out. Since getting it fixed about a month ago, it's been running perfectly, no stalling, no rough idling, nothing. It actually feels more responsive than before, and the engine's purring like a kitten at stoplight. Definitely worth every cent I spent on it. Honestly, such a relief to have it sorted. You know how these things can drive you crazy when they're not working right! Haven't had a single problem since the repair, and the engine light has stayed off. If your symptoms are similar to what mine were, I'd definitely recommend getting it checked out sooner rather than later. These things tend to only get worse if you leave them.

Thanks for the detailed follow-up! That's really helpful to know about the cost and the dual issues you found. After reading your experience, I actually bit the bullet and took my car to a mechanic yesterday. You were spot on, they found similar problems with carbon buildup, and the idle control valve needed work too. Got it all fixed up, came to about the same price range you mentioned. What a difference! The car's running incredibly smooth now, no more of that annoying stuttering at red lights. Really glad I didn't wait any longer to get it checked out. Thanks again for all your advice, definitely saved me from more headaches down the road. It's such a relief to have this sorted out. Guess I've found my new go-to mechanic too, they were really thorough and explained everything clearly.