Oil pressure

[achoeypatkul@hqfaus01.unicef.org (Amnat Choeypatkul)]

     Hi everyone,
     
     Here are my other two problems.
     1) Whenever I started up the engine--'89 Audi90, at the beginning, the 
     "oil pressure" gauge kicked up to almost maximum--about 5 bar.  Then, 
     after 10-15 mins (or when the "oil temp" gauge hit 60F degree), the oil 
     pressure will automatically drop to about 1-1.5 bar.  (I'm using 10w-40 
     oil.)  The questions...
        - What is the "normal" oil pressure on the Audi90?
        - What is the Audi recommended oil grade?  (I couldn't find it from 
     the owner manual.)
        - Is it normal /or OK to have such a very high oil pressure when you 
     started up the engine?  (If not, could you pls tell me what should I do 
     to correct it.)
     
     2) My engine (just had 60K maintenance/service) always knocking when 
     the engine is cold and lost its power.  (I had a small garage did the 
     "compression test" on all 5 cylinders, before I bought it a month ago, 
     and the results were 200-195-200-195-200 psi.  What is the ideal/normal 
     pressure (psi) for the compression test should be?  Pls Comments.)  
     Right now, I suspect the "Ignition Timing" is not setup properly.
        - Is there any other place which may cause this "knocking" & "Lost 
     of power" I should look into?
     
     Many thanks,
     Nat