Volvo S80 Engine Revs Up

The Rpm Is A Little High But It Still Under 1000 Rpm,,it Doesnt Do It All The Time ,,it Comes And Goes,,why?

When Driving (mostly On Freeway) Rpm's Jump Back And Forth 2000 To 2500. Car Jumps A Bit. I Apply The Same Pressure To Gas Pedal, But Rpms...

Engine Revs While Idling It Goes Between .5 To 1 And On Some Occasions It Has Revved Up To 2 And Then Dropped To 0 And Stalled

I Have Been Working On A Volvo That Has Not Been Ran For 4 To 5 Years. I Have It Started And Idling Well, However When I Press The...