On my '99 Montero Sport ....when going around 30 to 40 MPH the RPM's jump up and down between 1200 and 1500 rpm's. You can feel a bit of hesitation when this happens.
The sport has about 72,000 miles on it.

It ridesfine on the highway.

Any idea's??

 

Can you describe this a bit more? Are you giving it gas when it does this, or coasting?

MY first thought is the transmission (shiftingto4th and back to 3rd), have you had the fluid flushed as recomended? How about the other maintenance (plugs, wires)?

 

I'm just coasting......and I think it's in the 4th gear but doesn't like the lower rpm's in 4th gear. It runs fine if I manually put it in 3rd.

I'm probably due for some basic maintenance.

I asked the same basic question with a little more detail.on this forum back on Aug. 9 under the headline "Rumbling noise".....but didn't get much response

benchman

 

Yeah my 4th gearis pretty worthless at 30-40 MPH, it may be shiftingup automatically to 3rd??

You say it's jumping up and down, does it do it many times at once - up / down, up / down, up / down or just once? If it is continuous you *may* have a vac leak.

Your comment of "Im probably due for some basic maintenance" makes me think you need to catch up on that before troubleshooting too much.

 

The rpm's go up and down about 3 or 4 times in the stretch of a block or two then I'll either break or slow down (small town driving) or speed up.
It's annoying (mainly to my wife!).........she bugs me about it.

I'll see about getting some maintenance done and then see how things are doing..........Thanks!