My 850 turbo balks for a second or so when I hit the gas. Getting lousy mileage - about 14 mpg, used to be 18-19 mpg. 210,000 miles. Could it be the regulator or the vacuum line to the regulator? Also, once in a while it refuses to start, but will after about 5 - 10 minutes. Seems fuel related - a few catches but doesn't start. Also, what effect would a bad fuel injector exhibit?

 

Before you get into any other diagnostics when was the last time you did a stage "0"