a mis at 2000revs on my 07 zafira 1.9 cdti 120?

I took my 07 zafira 1.9 cdti 120 in for a service about 2 months ago and since I had it back there's been a sort of mis at 2000revs in all gears, taken it back to garage twice and just seem to be fobbed off, it'll run through(air in fuel filter), air flow meter, it sound fine to us, all different people at the same garage. any ideas???? Can any one help solve my problem?????????????????