How do I replace the idle control valve on a 1988 BMW 325i?

To change the idle control valve disconnect the wire harness from the valve. Take off the 10mm nut that holds the mount to the intake manifold and pull the mount clear of the stud. Pull off the tube that goes to the intake manifold and then pull the idle control valve from the intake boot. It's a good idea to completely remove the boot and examine it for leaks. The rubber on these boots gets dry and cracks over time and allows extra air in the system behind the MAF wich confuses your car's brain.