After a 2 hour drive with no problems at all when I pulled in the driveway and put it in park, the engine RPM began to surge from 700 to 11-1200 and back again in a random pattern. No engine temp, charging or other issues noted and no codes thrown. A quick check under the hood didn't reveal anything obvious. Any ideas?

 

Dirty IAC?

 

Check the vacuum line from the manifold to the brake booster, including the plastic elbow that connects to the brake booster.

 

Thanks for the help, guys. I wiggled aroud all my vacuum hoses to make sure they were tight and then started it up. No surging! Looks like it's fixed - for now.....