Could too many idle connections affect PostgreSQL 9.2 performance? Some queries on my database server seem to take a long time to respond, and I believe the CPU usage is high.  When running ps aux, I see ~250 "idle" connections (which I believe to be too many).  I haven't started doing a full diagnosis, but I wanted to know if this is a good place to start looking.

I am also using PgBouncer with transaction-level pooling.  I am suspecting that I can easily reduce the number of idle connections by tuning the pool size.  However, I don't want to start doing too many changes unless there is a good reason to do it.

Can many idle connections in PostgreSQL 9.2 affect performance?

Thanks very much!
I seriously doubt idle connections are your issue.  PostgreSQL is very capable of handling idle sessions since they take almost no resources.  Active sessions on the other hand are much more likely the cause of slowness.

See https://wiki.postgresql.org/wiki/Number_Of_Database_Connections for reference on the number of database connections.