P38 stutter

Hi fellow members, I have one of the last P38 (registered 2002) 4.0 Westminister so I have been told, the car has now done 104,000 miles and has created a stutter, just passed MOT with two new lambada sensors fitted, it has been conversted to LPG about 70,000 mile ago when I bought it, any suggetions welcomed, thanks Steve

Ht leads - get some new good quality ones - Magnicor or similar.