What would cause my 1993 960 to have an erratic idle. RPM goes from 350-800 at ldle? Also at steady slow speeds, under 40mph the engine will surge. Non of this happens when the gas tank is at or near full. Could it be a fuel pressure regulator? Car has 224,000mi, and runs great otherwise.

 

Any codes?

 

No codes are displayed.

 

When it happens you need to try to get under the car Safely and inspect the hoses in the Rear of the car good.
The Tank lines for the Evap system sometimes collapse. That will cause it.