As far as I know, the Idle Control Valve is preset at the factory. I have never heard of a procedure for adjusting the ICV. Basically, it either works or it doesn't. It is possible for the the valve to become clogged with debris so sometimes they don't close 100% thus allowing too much airflow. This is why it is recommended to remove the ICV and either spray some carb cleaner into the valve end or to soak the valve portion in carb cleaner. One way to positively check to see if its got a tight seal would be to cap off one end and then apply a vacuum on the other end using a hand vacuum pump.

Unplugging the 3-prong TPS connector should raise idle by around 300 RPM. If you unplug the connector and nothing happens, this points to either a defective TPS, a bad ICU, or a bad ground connection (middle pin) on the TPS female end of cable. (see my previous post for testing the TPS). Possible causes for a defective TPS include a chaffed or broken wire in the cable, dirty switch contacts, misaligned switch, or internal switch malfunction. If you would like to see what the TPS looks like see:

http://oem.thepartsbin.com/parts/thepartsbin/wizard.jsp?year=1991&make=MB&model=560-SEL-001&category=All&part=Throttle+Switch


T.C.