Volkswagen Repair: Loss of power, restriction of RPMs, oil pressure gauge, vw cabriolet

Question
Ok, I have a 1990 VW Cabriolet, it has about 150 K on the motor, and it has had a large loss of power, and only lets you rev the motor up to about 3500-4000 rpm's. I had the fuel filter changed, and the air filter is clean.  The oil pressure gauge also shows a loss of oil pressure.  I had the timing checked, gave it a tune up, and an oil change.  My mechanic doesnt really know what it is, maybe you could point me in the right direction?

Answer
Matthew,

Did your mechanic check the fuel from your old fuel filter?
If not remove the new filter and drain the gas into a clean jar.  If the gas is rusty, you've got fuel contamination, and will need to check for more damage at the control pressure regulator, fuel distributor, and look for rust at the injectors where the lines attach.  Your tank or filler neck may be the source of the contamination.

Check your compression as well to determine the loss of oil pressure.

Good luck,

Paul