Just wanted some ideas as to the most common sources of both the above codes (lean fuel rail pressure) occurring at the same time along with the intermittent display of "Restricted Performance". No noticeable change in running or idling smoothness or speed, car starts normally. Have recently changed MAF sensor in response to same code but it returned today. Fuel pump also recently replaced due to failure.
Any and all ideas welcome

Forgot to mention: 1999 Vanden Plas, 114000 miles.

 

Hi,
Did you mean to write P0171 & P0174 ? If so, I'd start looking for an air leak. You can check the fuel trims to see what's happening. Many threads on here about these things so I recommend a search.

 

Attached is a really good article on how to decipher the fuel trims.

 

Look for a leak along the tube from the air filter to the throttle. Lots of info on both banks too lean. Hole or tear in the air tube, or loose connections the frequent cause. Might also try a can of a good fuel system cleaner (SeaFoam or Gamout's equivalent. Also try tightening the bolts on the intake manifold.