RPM jump during decel/braking

[balk14]

Hi All,

Have come to notice something odd which started in the last day or so -

While slowing to a stop or generally coasting, my rpms jump from the 1k range and will occasionally spike to 3k before slowly coming back down - the engine is also revving during this time.

Everything else seems to be running fine, no hesitation or sluggish running/acceleration.

Any ideas???

Thanks everybody

[nike001]

Are you sure the car isn't just downshifting?

[RITmusic2k]

Could you possibly rephrase this and ask again? I'm not sure what you mean when you say "the engine is also revving during this time"? You're referring to the engine revving as if it were a separate phenomenon, but by describing the 1k rpm -> 3k rpm spike, you're giving us the actual measure of engine revving.

Also of interest:

Are both feet off the pedals when you observe this behavior?

Is your car an automatic transmission?

[balk14]

sorry for the confusion...all signs would point to me actually pressing the gas pedal as if i were accelerating...but ive observed this when both feet are off the pedals as well as when i apply the brake --> mph are decreasing but rpms suddenly spike momentarily, then head back to normal levels

The car is an automatic - if this is a natural occurrence for a downshift then I apologize in advance for wasting time!

[az3579]

sorry for the confusion...all signs would point to me actually pressing the gas pedal as if i were accelerating...but ive observed this when both feet are off the pedals as well as when i apply the brake --> mph are decreasing but rpms suddenly spike momentarily, then head back to normal levels

The car is an automatic - if this is a natural occurrence for a downshift then I apologize in advance for wasting time!

Sounds like it's just the auto downshifting. A way to test this is to put it into manual shift mode (push the gear selector to the left into the +/- zone), keep it in a gear, and then brake or take both feet off the pedals to see what happens. If it doesn't do it, it's probably just because it's staying in gear as per your request by putting into manual. I would rev it up to a higher rpm when you do this to make sure the revs don't get too low, as I believe the auto downshifts automatically if the revs get too low regardless of what gear you're in.

[balk14]

ok ill give it a shot ^^^...but if it is just a downshift thing why does it only happen once in a while and not every time i decelerate??

[RITmusic2k]

It could be that you're noticing it happening part of the time because you're not always slowing from the same speeds or slowing *to* the same speeds every time. You may have to experiment to find that this is a repeatable phenomenon, e.g., you notice it always happens when you slow from 40mph - 20mph, but not when you slow from 50mph - 30mph.

Also, in your estimation, is this something that's definitely different in the last day or so, or could it be something the car has always done but you've only now become aware of it?

[Hermes]

Do you notice it everywhere or just specific roads? Mine downshifts all the time on hills, pisses me off so I remember to put it in the "manual" mode and choose the gear I want. Natural part of driving a step, I'm gonna get my tranny software reprogrammed, hopefully will solve that

[balk14]

It definitely is something that just started happening recently...I remember exactly the first time it happened and I thought it was really strange. I was going about 10 mph headig into a stop at a red light. It happened today when I was going about 50 thru a curve...its not an exclusive event from what I can tell. Is there a chance my gas pedal is getting stuck occasionally or something of that nature?

[Hermes]

I don't think the pedal sticking would cause a downshift... Maybe there might be issues with the tranny software

[az3579]

Hmm...

You said it does it even when your foot is off both pedals. Do you feel the car accelerate a little when it does it?
If you do feel it accelerate a little when it happens, there could be something else there causing it; idle control valve? I'm not sure if E46's have those, but it's what caused it in my old E30. Every time the rpm's surged, the car accelerated a bit on its own. With an auto, it's always in gear, so I would think the car would accelerate a bit when the surge happens and you're coasting...

[balk14]

ill have to take it out for a drive today and pay attention to that...thanks for all the help!

[MrMaico]

Just curious if you ever figured this out?