RPM variation Motor John Deere Retroexcavadora

I have RPM problems in the Jhon Deere Retro Mod 310 D. Discard the injection pump in the test bank and installed it in another machine and works perfect. What could be altering the rpm in empty that tends to climb without moving anything, that is, empty and reluctant but increases its rpm until it reaches 1500 and a little more sometimes ???

Some false air entry is made of a tune from the revolutions, the air is the oil system also occurs a similar failure but the RPM does not supply if they oscillate.

Ok. Thank you, we will review the subject.