How do you diagnose 1993 940 no turbo runaway engine rpm Can't throttle down?

Engine speed is controlled by how much air is admitted. There are 3 ways for air to get in; # Open throttle valve: Look for stuck linkage, throttle cable binding, foreign object stuck in the throttle plate, etc. # Idle Air Control valve: There is a ~1 jnch dia hose that bypasses the throttle. The valve in the hose can stick open and cause either no idle or fast idle. Try cleaning it with carb cleaner. If you have over 200,00 miles on the car the brushes in the valve motor may be worn out. # Air leaks: Listen for a sucking sound with a piece of hose held near your ear and the intake manifold. If that doesn't help look here; http://www.brickboard.com/FAQ/700-900/