My wife uses our 2005 XC70 (78K miles) as her daily commuter. Last week Culver City Volvo did a THROTTLE BODY CLEANING ($462). Since then she's been reporting a noticeable throttle lag at highway speeds. I took the car in today (she's driving my '98 XJ8 that she doesn't like so much) and was told that a code came up that indicates the FUEL PRESSURE SENSOR is likely to fail. They want $521 to replace it.

Should I go for the new part or just keep running as she is? Feedback greatly appreciated!