My Jeep has had problems idling for quite some time now but I finally decided to do something about it.
One evening after getting home I tore the air intake off the car to check out the IAC valve.
The IAC controls the idle of the engine when the foot is off the accelerator and the computer needs to mix a precise amount of fuel and air to keep the car running while at idle.
My IAC valve attached using one screw but was fused in place by 14 years of carbon deposits. It took a LOT of persuading for it to come off. I really thought I might break it while pulling on it as hard as I did but eventually it pulled loose. Use pliers if you have to but be very careful to not destroy the electrical connector which has a plastic housing.
You can also just replace the IAC altogether. Some cost more than others. Ranging from ~30 to $90. If you have a BMW it’s probably a cool grand and requires 14 special tools and a computer to install.
If you replace the IAC with a new one, the computer in the vehicle is going to need to “relearn” the fuel / air mixture curves. Your car is very smart and does this type of calculus on the fly. However be prepared. If you don’t reset / relearn the sensor with a scan tool, your car is going to have to learn while driving and the first 5 minutes or so your car is going to run terrible while it sorts things out.
Happy cleaning! Hope your car runs better!