Would be greatful for any help. I have a 06 focus st3, had it serviced recently(new plugs,oil,oil filter)but noticed that it has developed a shudder when accelerating hard in gears at about 3500-4000 rpm at peak boost more noticable under load when there is three people in the car. It also feels like it has lost some torque. I also have a Graham Goode induction kit which i have cleaned myself with a K&N filter cleaning kit and the car was remapped approx 1 year ago, car has 54k on the clock. Any suggestions would be much appreciated.

 

Car runs fine other than this issue, it's not bringing up any fault and doesn,t go into safety mode

 

Had a few responses saying that I might have over oiled the air filter which may have contaminated the MAF sensor could this be the fault. Also the say that denso iridium plugs in an ST (remapped) are a no go as they cause a misfire under high boost could this be the fault. The problem is prob simple as it only occured after the service. Any suggestions would be greatful.