[JoshmkII]

damn, finally got it last night, and so far I have almost 400 miles on it. :P

stupid question time, I searched and couldn’t find anything, and the dealer had no clue either..

here goes...

When I get on the gas, then let totally off the gas and depress the clutch, the rpms climb up about 400-500rpms before dropping. Is this supposed to happen? The only thing I can think of is that it is supposed to happen to help keep the power up... It doesn’t happen unless I put the clutch in.. And yes, Im 100% sure Im off the gas.

[MY_SUV]

It's caused by the "fly by wire" throttle control. The gas pedal is not mechanically connected to the throttle.

I noticed this as well. I did find that it decreased over time. Not sure if it's the ECU learning or the driver learning.

[M]

WTF?!
So what is going on there, is it actually better for the engine to keep revving a little longer after the pedal is released or is this just a glitch in the "fly by wire" programming? The main attraction of the "fly by wire" throttle is quickened throttle response, which is obviously, when depressing the pedal but shouldn't it also quicken throttle response when releasing the pedal?
I'm completely baffled....

[MY_SUV]

The main attraction of the "fly by wire" throttle is quickened throttle response, which is obviously, when depressing the pedal but shouldn't it also quicken throttle response when releasing the pedal?

My feeling exactly. Recently had to remove the neg cable from the battery to do some work which also reset the ecu. I noticed that "rev jump" after letting off the gas again. I believe there is some ecu learning that decreases that.

[Ender2664]

I know what you are talking about, it is a bithc when you shift at 7k cause it takes a while for the car to learn so when you have like 2k miles on her and you pull a 7k shift and you are not careful the revs will shoot deap into redline, as my friend showed me. But anyways, just learn the car and let it learn itself, and i have 4k miles on her, and i dont have that problem at all anymore.

[JDiesel]

I don't think it's a problem with the fly-by-wire programming, just a function of remaining gasses in the engine and the inertia of the turbine in the turbo. When you get off the gas and push the clutch in, you're decoupling the engine and tranny. However, since there's still exhaust gasses flowing through the engine, and the turbo won't stop spinning immediately since it has a ton of inerita, it will continue to spool, creating boost in an unloaded engine. The recirculation valve redirects most of the air, but there's still some exhaust gasses left that need to be vented. So basically, it's like blibing your throttle at idle. If you guys are really on the throttle, it's really noticable (RPM jumps up on mine about 500 RPM) since there's a lot of boost. But if you're tooling around town with little to no boost, the RPM doesn't jump up when you shift...

[Rev]

I think the reason the revs shoot between shifts is simply because of physics and inertia. Without sounding nerdy, your clutch is connected to your drivetrain.

When you depress the clutch, the drivetrain is disengaged from the engine flywheel. During this disengaging point, the flywheel is still rotating and still has a pretty high moment of inertia, but it doesn't have the drivetrain load. This then causes the engine to slightly overrev because you've removed the drivetrain load from the engine.

[Ender2664]

If it was just due to what you are all saying it is than that would be ture of all turbo cars, and it isnt. I have driven many turbo cars and none of them have that problem.

[ss3homer]

I am almost postivie that thunder is right. I completely agree!

[MY_SUV]

I too would agree with Thunder except for the fact that it changes over time. And when I reset the ECU, it went back to the way it was.

I really don't know though..............

[crashsti]

um...why does everyone shift at redline? at 7000rpm you'd be way past the horsepower peak and in the red by the time you complete your shift. there is a phenomenon called valve float that occurs at redline and is usually a determining factor as to where redline should occur. i have my rev light set at 6000rpm just to be on the safe side. there are occasions when you can't watch the tach.

[Rev]

Out of the top of my head, the best shift point will be around 6500rpm, because when you shift into the next higher gear, your rpm's will drop below the peak HP (maybe 5800?) ... That way you will be gearing up your next shift towards the peak HP.

[Fhqwhgads]

Someone mentioned that this was intentional programming of the throttle by wire for emissions. Basically, when you let off the gas quickly, that's when the car will produce a lot of combustion byproducts (I'm not sure if it's unburned hydrocarbons, NOx, or some other nasty), so the throttle is programmed to stay on a little longer in order to clean things up a bit. I'm not sure if the idea is to protect the cats or if the extra emissions would make it through the cats.

Has anyone else noticed that when they're coming to a stop and you depress the clutch early (say at 40 mph when stopping completely to zero) the rpms will stay pretty high (around 1000 to 1200 rpm) until you come to a complete stop, then they drop?

[bitabur]

Maybe its to be friendly to the synchros if you decide to downshift.....

[Digitalfiend]

Originally Posted by Fhqwhgads

Has anyone else noticed that when they're coming to a stop and you depress the clutch early (say at 40 mph when stopping completely to zero) the rpms will stay pretty high (around 1000 to 1200 rpm) until you come to a complete stop, then they drop?

This happens with my RSX as well but not consistently. It is weird.

BTW I just noticed the post that said if you shift at redline your RPMs fall to above 5k? I would have figured the STi would be geared to fall closer to 4k? If that isn't the case you must have to shift a LOT in the STi and probably explains the low trap speeds.