my st170 felt very slow when the imrc wasnt working made it much better after i repaired it

one thing i would double check is make sure the warning lights are working on the clocks when you turn the ignition on as the lambda sensors and imrc are common faults and both cost £££ from dealers to put right i get around 25 mpg out of mine thats mixed driveing day to day so a bit more than most in its class to run but they are a nice all round drive tbh quick enough not to be board great handleing sound fairly good cant fault mine hope this helps mate