What year is your car? That part number is correct for an '87-'89 for sure. You can always try and buy a used one.

Not for nothing but have you considered removing the switch and cleaning it up. I think it is a just a simple micro switch. Maybe some dust or gunk got stuck in there causing a constant contact???

$186 is allot.

Here is a new one on eBay for $79 Porsche 911 throttle body micro switch. Fits 84-89 911 PN# 911 606 013 00

It is a 1988.

The 911 606 013 00 seems to be for the Turbo. Apparently the non-turbos have to get the 013 03 version. I don't know why the Turbo sensor is less than half the price though. :(

Idle Position Micro Switch
 

I had the following happen a single time last thus. as I headed out for a long drive to a track weekend. After normal start and misc. drive from home and through town and several lights, engine started to surge meaning on about a 5 second cycle was by itself going from 1000 to 3000 rpm up and down. Regardless if I was stopped or driving along which of course meant I could feel it in the throttle still happening.
I got to a place to stop after 20 minutes and shut off the car, got out and looked. See nothing unusual on the throttle. Started the car and watched the throttle and revved the engine manually, condition was gone. So I drove 1200 miles in 4 days and did a track weekend in GA with no recurrance.
I thinking maybe the throttle microswitch may have been stuck closed during that first occurance, then it managed to unstick. Or, turning the car off re-set something electrically maybe ?? Since this was happening when I was stationary, a stuck microswitch telling the ICV to idle correctly was not happening either so it can't be the entire problem. After this, the car idled decently even with the AC running.