Try taking the gearbox sensor lead out ( held in the underneath of the gearbox by 3 x 10 mm bolts) give it a clean & put back in, make sure its tight & the gap between the flywheel & the head of the sensor lead is correct, 0.4 -0.8mm, larger the gap ( within spec) the better in my experience.Good luck! let us know if you sort the problem & if you dont!