Why are IDLE connections using cpu according to TOP.

I have an overloaded DB and I see several IDLE connections that are using significant CPU.. (Not Idle in transaction)
Why would an idle process be eating so much cpu? Or is it not actually idle?


Here is an example from pg_top:

last pid: 11821;  load avg:  6.11,  6.32,  7.64;       up 1+21:05:31
50 processes: 3 running, 42 sleeping, 5 uninterruptable
CPU states: 21.7% user,  0.0% nice,  7.8% system, 46.9% idle, 23.6% iowait
Memory: 29G used, 149M free, 13M buffers, 27G cached
Swap:

  PID USERNAME PRI NICE  SIZE   RES STATE   TIME   WCPU    CPU COMMAND
 4779 postgres  20    0 4383M  573M disk    3:16  4.79% 39.42% postgres: gpup gpup 10.202.99.5(46391) UPDATE                                                                              
11591 postgres  20    0 4383M  108M sleep   0:12  2.08% 19.61% postgres: gpup gpup 10.202.99.6(52459) idle                                                                                
 4191 postgres  20    0 4384M  709M sleep   4:33  2.50% 19.41% postgres: gpup gpup 10.202.99.6(42288) idle                                                                                
10942 postgres  20    0 4383M  242M sleep   0:42  5.08% 16.86% postgres: gpup gpup 10.202.99.5(58373) idle                                                                                
10930 postgres  20    0 4390M  281M sleep   0:43  1.62% 15.30% postgres: gpup gpup 10.202.99.6(52273) idle                                                                                
11571 postgres  20    0 4390M  210M run     0:25  4.32% 14.51% postgres: gpup gpup 10.202.99.6(52455) SELECT                                                                              
11533 postgres  20    0 4383M  109M run     0:14  2.31% 12.75% postgres: gpup gpup 10.202.99.6(52453) SELECT                                                                              
 7494 postgres  20    0 4384M 1611M disk    2:31  2.44% 12.35% postgres: gpup gpup 10.202.99.6(53620) SELECT