x3 tps most likely needs adjustment, if your explaining what i think your are, does it only do it when there's no pressure on the engine.. when in neutral or clutch in... couse i had a buddy with the same thing but it never did it while we was actually driving it (it was always in the 1k-1.5k rpm range). his engine was good, and strong, and since it didn't do it while he was driving he never cared to fix it.