Rpms jumping 15-30 second intervals
2000 ranger xlt, 4.0 v6. This has been happening for a few years now. at random times while driving the RPMs will jump up 600-1000 and stay there for approximately 15-30 seconds, and the truck gets noticeably louder and if it does it while I am stopping, it's not easy. I used to have a tempo and when I got a vacuum leak, it acted exactly the same, only it was constant, so I'm not sure what it could really be. I'm not sure what the fuel pump in these trucks is like, but i know some vehicles have a two speed fuel pump, so maybe if these have the same thing, it would seem as if it is kicking into the higher speed at random times. Has anyone else had this issue? What other things could it be? Thanks for any information!
00 Burnt Orange Ranger XLT