automatic gear select does not work well

I think you got water into one or more electrical connectors while steam washing. I'd be looking at the throttle position sensor (TPS) and the connections on the transmission, also any other sensors on the engine you can see and easily get to. Sensor problems can really affect transmission operation. Try the TPS first. It's on the throttle body on the intake manifold. If you want t see a Nissan specialist, here's a directory link for you: http://repairpal.com/nissan-repair-in-lake-in-the-hills-illinois