Have just purchased 59 plate 308 hdi. Pleased with car just one small problem. At 30 mph in 4th and 5th gear I sometimes get a judder from the engine under a slight load and the rev counter fluctuates between 1100 to 1300 revs. Any advise will be helpful. The car is still under warranty but I have to pay for diagnostic at a cost of £40.00 which I can do without. Please help if you know the answer to this problem.