Hi there
As dchartier stated you must call FB41 from OB35.
Default time of OB35 is 100ms so set the cycle time 100ms.
What the previous person has done is wrong, he probably left the cycle time blank because FC is always called at diffrent time interval so he might have decided to leave it blank ;-)
Values for Gain , TI, TD depends upon your process, change there values and see if things are improving, you won't bust anything unless the process is very critical like controlling radiation pressure in Nuclear chamber ;-)