[xeroinfinity]

Welcome to AF !

How deep was the water he drove thru ??
Does it shift if you manualy shift the car ??

Iit sounds like somethings still wet. A plugin down under could be soaked and is shorting everything out.
Check the plug ins on the trans main harness, and any other that might have got wet.

Also is thier any signs of water being in the trans ??
And you might check your vacuum lines for the fast idle, one could be loose/cracked or sucked water into it.

Good Hunting