>>
>>The idle switch is more critical for idle/low speed smoothness.  
>>Don't blow this one off in the adjustments/tune-up.
>>

The idle switch is for emission control purposes. If the paddle is completely
released while the engine is still at high revs (higher than 1500 RPM), the
switch tells the computer to shut off fuel completely. When the engine RPM
drops to below 1500 then the fuel supply is resumed. This reduces waste of fuel
and so does the emission.