The microswitch on the 603's is on the throttle mechanism, it is only there to trip the A/C off at WOT.

There is a throttle position sensor inside the IP itself, but it has more to do with the EDS controlling the EGR valve than anything else. Emissions controls.

With the plug removed from the back of the IP, idle speed is completely mechanical and should be low (~450-500 RPM). Any higher and something is out of adjustment or sticking in the linkage assembly.

Looks like the OP found gummy ball joints and a sticky cruise control. Both very common issues on these engines.