1999 Forester RPM jump when cruising downhill

esciaky

Hi - I recently bought a 1999 Subaru Forester and noticed the same issue twice, under the same conditions. From poking around, I believe this maybe a "surging" issue, but not really sure (and the term is new to me).

Issue: when cruising down a steep hill on the freeway and laying off the accelerator, the RPMs jump (between 3-3.5K) and I hear the engine working/noise increase as if I was starting to hit the accelerator in neutral. This happened twice in the same trip, under the same conditions. Each time, the RPMs lowered to normal levels within 5-10 seconds.

A few (maybe relevant) pieces of context:
- Car was full of people and gear (ie. there were weight considerations)
- AC was running
- The accelerator was not being pushed at all either time
- Have not experienced any other "surging" or RPM, transmission issues in any other driving conditions
- automatic transmission, 168K mileage

Any thoughts or suggestions are much appreciated. Thank you!

kyfdx

esciaky said:

@kyfdx & @Mr_Shiftright

Quick followup question:
- in looking at the owner's manual linked below, I don't see that there's and O/D feature in the '99 Forester (but maybe missing it). I did a little digging but wasn't quite sure, is it actually possible that when the transmission is in D under the conditions I described, the transmission will automatically downshift (as a form of engine breaking)? Or, will the transmission only downshift if I switch to 3,2,1?

http://www.manualslib.com/download/232298/Subaru-1999-Forester.html

Thanks again

In general, plenty of automatics will either hold a gear, or downshift, when heading downhill under no throttle or braking. I can't speak to your Forester specifically, but that seems to match the action you described.

kyfdx

Does the engine surge, or is it the transmission downshifting?

Mr_Shiftright

Good point. You might try the "O/D off" button next time and see what happens.

esciaky

Thanks, both for the quick response.

@kyfdx - the car and term "surge" are both new to me, but to your point, maybe what I was experiencing was a normal downshift given the downhill conditions. I think the combo of the engine noise and RPM jump (w/o using the accelerator at all) made me feel like something was wrong.


@Mr_Shiftright - I will try that.

Appreciate it!

esciaky

@kyfdx & @Mr_Shiftright

Quick followup question:
- in looking at the owner's manual linked below, I don't see that there's and O/D feature in the '99 Forester (but maybe missing it). I did a little digging but wasn't quite sure, is it actually possible that when the transmission is in D under the conditions I described, the transmission will automatically downshift (as a form of engine breaking)? Or, will the transmission only downshift if I switch to 3,2,1?

http://www.manualslib.com/download/232298/Subaru-1999-Forester.html

Thanks again

esciaky

Thanks again, @kyfdx !

Mr_Shiftright

Well if there's no "O/D off" on that model then yeah, drive downshifting manually as this is happening--I mean as you notice the revs go up on the downhill grade If downshifting doesn't change anything on the tach, then the transmission has in fact downshifted already going downhill.