Theirs lots of things it could be ... It would of probably happened even if you didn't visit the car wash, its just badluck it did happen after, because your probably thinking water got in some where it shouldn't have, but here's a list of things I changed, with No.1 being the last thing I did which sorted my car out last year when I had the same problem.
1. Crank Sensor
2. ISV Valve
3. HT Leads
4. Spark Plugs
5. All the little breather tubings (really thin ones)
6. ECU Relay