CX9 RPM sticking up when in neutral

[mo01]

have anybody noticed or found that the CX9 RPM's stay up when the car is moving even if the shift is in neutral, all other cars RPM will go down to idling range (600-900 rpms), mine 2009 CX9 touring keeps the RPM matching the car speed.
this is how I found it, I live down on a hill from the main road, and I put the car in neutral to go down, I noticed the RPM going up instead of down as I gained speed down the hill, then tested it at highway speed on a long hill, same result RPM needle went above 2K RPM going at 50 MPH in neutral.
My concern is that as everything being electronic, that means the computer doesn't really care much of my actions (shifting to neutral) or the RPM gauge is not actually showing the real RPM from the engine, either way is not comfortable.

 

[ceric]

Are you sure about "all other cars RPM will go down to idling range"?
The momentum of the vehicle will carry the RPM up depending on which gear your CX9 is in. All that vehicle I have owned did that.
I once pushed the shifter into N by accident with my BMW. It shot all the way to redline (around 5600rpm) at 70+mph. Shifted it back to D, and the RPM dropped back to normal.

Also, when going down hill, you should not use "N" and rely on the friction brake alone.
A short trip may be OK. For a long downgrade, please use engine braking (down shift to 3,2).

 

[mo01]

Are you sure about "all other cars RPM will go down to idling range"?
yes I'm sure.
you have to let go the gas when you shift to neutral, your RPM will spike if you are pressing on the gas and the engine is free from the transmission.
My main concern in the post is, as the engine is not longer moving the car it must go down to idling, if it doesn't something is wrong with either the computer or the dashboard, my bet will go with the computer. I'll be visiting the dealership thi weekend to see what they say, and probably will post it in the NTHSA website to see if they consider it normal for a car in neutral to move up the RPMs by itself.
I've been driving all kind of cars and trucks for more than 25 years and this is the first to do that.

 

[ceric]

After some thought, the case of my BMW was probably caused by my foot still on pedal that was keeping it running at 70mph.

True, I see no reason mechanically, that in N gear, the rev should not be at idle.
Some kind of ECU programming at work here. I need to try it out myself.

 

[mo01]

update, just been at the service office, the mazda tech says, the RPM sticking up is normal for the CX9, he says the CX9 has something called slope assist that holds the RPMS to the matching range for the speed when in neutral.
I don't think I buy into it, but as they ruled as it is designed to be like that I don't have much arguments, I'll post the question now to the NTHSA and see what they say.

 

[mo01]

NHTSA correcting myself

 

[ceric]

I verified this. Indeed, thr RPM stays after shifting to "N".
However, I believe this is by design, though I can't be sure of its reason.
Mostly likely this is to maintain power-band while gear shifting to smooth out the transition of gear change.

If I were you, I would post a question at mazdausa.com. They usually reply within a week or two.

 

[jabba]

I wonder if it is indeed by design, because I remember something in the owner manual saying that we should not shift into neutral while driving, since it could damage the transaxle. Would keeping the RPMs high lessen the driveline shock when putting it back into Drive?

 

[ceric]

>> Would keeping the RPMs high lessen the driveline shock when putting it back into Drive?

I am guessing THAT is the reason for keeping the rev because the next logical move is to put it back to "D". This is assuming that putting into "N" was by accident.

There is a great debate on the web about whether there is indeed any benefit in putting it in "N" nowadays with modern vehicle when going downhill or coasting.

 

[mo01]

this has been of great help, I agree that if by design it should be to lessen the shock when is put back into D.
I'll post the question to MazdaUSA, as I would like some assurance that is the purpose and that the ECU will not attempt to rev up at any other time (like while in D) by itself.
on the debate of D vs N, I'm on the fence, logic tells me rpm in 600 consumes a lot less than 1500-2000 down hill, and kind of same principle is used in hybrids by turning engine off and letting the electrical motors regenerate the energy with the tires rotation in free fall, but there is the other issue of the shock in the driveline when coming back to 'D'.
I live in a very long hill (about 1 mile) which I normally take in 'N' until I get to my home so car never gets back to 'D' but that is just me.
I'll keep this updated with the response from Mazda. But so far I think that I'll stop playing with the shifting into 'N'.