temporary loss of power/engine light

Hi all
I have a Saab 93 2.2. diesel, 52 plate, new shape with 122k on it, full history upto 90k.
I keep getting loss of power accompanied with engine light, power returns after a few minutes or sometimes seconds, engine ligh resets itself(after several start ups).
Has anyone any idea''s I can suggest to garage (non saab) that may point him in right direction and to save me time and money!
 
Thanks in advance.
 

Try EGR valve, its a valve for the exhaust.  Its happened on mine a couple of times.