Hello Raoul,
I have encountered this kind of unusually high CPU consumption due to Diagnostics Agents from time to time. Probably caused by jstart.exe process.
The very first thing I would do : updating LMSERVICE06P to the latest patch level.
NB : patch 5 is available.
Most of the issues I have experienced with RCA/MAI on different SP level were finally solved by a LMSERVICE or Wily patch.
Only problem is that sometime I had to wait for many weeks for the proper patch ;-)
Worth a try at least...
Sebastien