Stalling E90 M3

S65 engine without intake manifold

Today was one of those days that I was really exited to work on a car. It was an 2011 M3 that intermittently stalls. Another tech scanned it and there were no faults, so they did the usual procedure, which is to reprogram the car with the latest software…the magical fix for everything. Only that this time, when the guy who takes the cars on extended test drives for cases like this drove the vehicle, the engine died twice on him. Sooo, I guess that means it wasn’t the software, huh.

The next step was to ship the car over to me for diagnosis. Curiously enough, another 2011 M3 with intermittent stalling came in the next day, also with no faults stored. Fun times! After a lot of thinking what the fuck could be happening with this thing and theorizing and talking to my team mates on what could be intermittently causing this shit to happen, I decided the best way to go was to chase whatever controls the idle air system. I looked at the training manual and found there is one common controlling device for the idle on both banks, so this would make the most sense, then I noticed the tank vent valve vents into the idle air valve. If the valve stays stuck and vents when its not supposed to, it could cause erratic idling. There are so many things that could be causing this, and the more you think about it, the crazier stuff you can come up with. This is when I need to remember to KISS (keep it simples, stupid) and try the easy stuff first.

So I went ahead and replaced the idle valve and tank vent valve, and so far I haven't heard anything again from the car. It was worth attempting to do the repair after analyzing what may have been going ok. There are many people out there that have the same thing happening to them on the s65 and s85 engines.  I would definitely recommend starting with the idle valve/ purge valves. The s85 has two of each. It's expensive, but if you have these cars you need to be able to pay to play.

Throttle valves, throttle actuators and idle air valve piping

Idle air valve and piping that goes under throttle valves.