Electrical I Unplugged The Icv And Everything Died!?

My '97 3.8 'vert used to have a tough problem - it was a little hard to start, idled roughly at 400 rpm, and pressing the gas pedal would kill it unless you were very gentle. I had probed the MAF signal and it seems to be fine. I was about to probe the TPS sensor signal...
And then I had the genius whim to see if unplugging the ICV would change the idle.
Yeah, it did.
Instantly, the car died. I heard a faint pop. All the dash lights went out. Turning the key doesn't produce any response at all - no dash lights come on, no turn over, no nothing.
I checked the fuses in the underhood fusebox and they're all okay.

Anybody got any idea what I killed?

wmburns - Thanks much, that's exactly the specific sort of info I was hoping for. I'll get another crack at the car this week and will post results.

Where is the PCM fuse? I pulled and visually checked all the fuses in the underhood fusebox and in the box under the steering column, and they're all OK...

Well it's been a while but there's news: It wasn't the PCM fuse, so I replaced the PCM with a used model from an online retailer - and that fixed this problem.
Note to self, don't unplug any sensors from a Mustang while it's running - on peril of your PCM's life!
Thanks WMBurns.