Check Engine Light

Hi,

I recently purchased a 1999 Turbo S with only 44000 miles on. I got this from London and drove home fine.  Since then the Engine check light comes on intermittently. If you rev over 4K it 'mostly' comes on.  It can stay on for a few seconds or for 10 mins + but does always seem to go off at some point.  I took this for a major service at a local Subaru Specialists (AdgeSpeed) and he didnt mention anything.  Could this just be a fault connection or do i need to get this properly investigated. I got all oils changed (Diff oils as well) except gearbox oil.  It does seem a little hesitant to change down.   Any thoughts would be gratefully received.

Many thanks

Dan