I have 90 Iroc with a 350TPI. Thee idle was fine before going to the car wash, maybe a little high around 800-900RPMs. I took it to the car wash and as soon as I was done the idle was jumping between 500 and 2000 RPMs very quickly and would eventually die. I also felt a significant amount of power loss like running on 6 cylinders or something. What would cause these symptoms from a simple car wash? After letting it set for a day it went back to normal. Any ideas?

This phenomenon is not uncommon. Possibilities include worn secondary ignition, water in blocking the reference hole of the O2 sensor, or corrosion on just about any connector that works most of the time and then gets iffy when it gets wet.

Whats the best way to narrow it down? Just by spraying water on all the sensors and vacuum lines to see if it recreates the same conditions?

Yes, you can test the cap & wires this way. Do it in the pitch dark and look for lightning strikes.