Originally Posted by Borren

Why wold i have a problem? no car as i know sold in sweden has this as a requirement

Its never been working like that on a evo in sweden thats for sure.

Originally Posted by evo 8 ya

So you can start your car while it's in gear with the clutch pedal out?? or do you have to make sure it's not in gear. If it was in gear with the clutch pedal out, your car would go cruisen cross the parking lot.

Originally Posted by evo 8 ya

So you can start your car while it's in gear with the clutch pedal out?? or do you have to make sure it's not in gear. If it was in gear with the clutch pedal out, your car would go cruisen cross the parking lot.

Originally Posted by THX1138

But yes, like you we can start the car with the gear in neutral and no clutch.

Originally Posted by titaniumkingpin

whats a APS dump?

Originally Posted by 93civEJ1

valve. I havent even worried with mine anymore. I just let it do its thing and see what happens.

Originally Posted by 90GSX-03EVO

To the people who are having this problem:

When you shift, do the RPM's start to drop, then they shoot up again on the tachometer or do they just jump up as soon as you press in on the clutch?

I've seen the RPM's drop and then jump up again during a shift, but that was on a modified car with tons of mapping issues. How is this problem happening on your cars?

Originally Posted by 90GSX-03EVO

To the people who are having this problem:

When you shift, do the RPM's start to drop, then they shoot up again on the tachometer or do they just jump up as soon as you press in on the clutch?

I've seen the RPM's drop and then jump up again during a shift, but that was on a modified car with tons of mapping issues. How is this problem happening on your cars?

Originally Posted by 90GSX-03EVO

To the people who are having this problem:

When you shift, do the RPM's start to drop, then they shoot up again on the tachometer or do they just jump up as soon as you press in on the clutch?

I've seen the RPM's drop and then jump up again during a shift, but that was on a modified car with tons of mapping issues. How is this problem happening on your cars?

Originally Posted by MalibuJack

I actually noticed this happen once with my car tonight.. what I did notice is that its much colder (more dense air) and I suspect my DV (A 1G DSM Valve) may not be venting enough air quick enough.. so the RPM's rise as additional unexpected air gets forced through the throttle body as the plates are closing....

Originally Posted by Turbocake

EDIT - please read the whole thing before posting a question.

I believe some folks are having different versions of the same problem, but I think that for the vast majority, my diagnosis is correct:

Unless the induction parts upstream of the throttle body are somehow manipulating the EFI's sensors in such a way that the Idle Air Solenoid is immediately cracked wide open (doubtful, because IAS's typically can't raise RPM's above 3k and they don't open all that fast), then none of the induction parts upstream of the throttle blade matter whatsoever.

The ultimate dictator of engine RPM is (air, via) the throttle body. If it's not getting in through this part (in an otherwise sound engine), it's not getting in, and RPM's will not climb. PERIOD.

BOV, Piping, all that stuff = Irrelevant - EXCEPT for mechanical issues - that we would ALL mysteriously be having in perfect unison - like the throttle spring, bearings of the throttle body, throttle cable, gas pedal, etc., there is nothing else that could possibly cause these specific conditions (RPM jumping between shifts) other than the throttle body being open to some significant* (<---more on this in a moment) degree to allow it to happen.

The gentleman, for instance, who said his gas pedal stayed down while the car pulled on it's own - that's definitely a distinctly different problem than what most of us are experiencing. I would say that car has something wrong with the aforementioned hardware-based issues - possibly the throttle body. Some throttle bodies made back in the day by BBK had a bearing tolerance issue that would only make the throttle stick when the car was running. Turn the car off and the problem went away. This was heard about, but not widespread.

With Evos, the fact that the symptons are so widespread amongst car and people types lends credit that it's an operation issue rather than an oddball problem for a few.

That said, let's get back to airflow. I've noticed that I had this problem after putting my mods on (Buschur stage II) and that it's gotten much worse since winter's cold air arrived.

I then decided to watch my AFC-II while driving around to get some hard numbers. (Boy do I miss datalogging with good software like EFI Live) and I noticed that when and where I thought was off the gas, I was not. I couldn't tell at all by feel, I had to see the numbers on the AFC-II to believe it. I tried modifying the timing of my shifts to what I thought would make the car buck from letting off the gas too soon, and it was perfect. Driving the car barefoot also helped my accuracy because I could perfectly feel the pedals.

Reasoning:

Boost is an incredible factor with our cars because the boost pressure is so high and the rotating mass of the engine is so low.

Check this out... start your car and rev it up. Watch your boost guage and see how much boost you get before you bounce the limiter... not much, right? That engine still revved way up and hit the rev limiter, right? Did you even have it all the way floored? Probably not.

Now, imagine the few moments in time when you've just "let off" the gas under boost. The concentration/density of air is much higher and much more air will flow through a given throttle blade angle. If you had magical boost just waiting, at full pressure all the time, your engine would free-rev so fast that you wouldn't be able to, at your FASTEST, snap the throttle all the way to the floor (nevermind all the way back up) before the engine spiked to redline. It's easy to see how even a few thousandths of a second could matter here. Face it, most of us aren't that precise at shifting, and this nuance exploits it perfectly.

Additionally, when you've let off, the density of that air may even slow the throttle blade down all on it's own - that's over two atmosphere's of air density in there and lots of flow forces acting on the blade actuation. TB bearings must be precise and smooth (under operating loads). The throttle spring is pulling against those forces and doing the chore of pulling your throttle cable (try rerouting it under the hood. I've noticed that the clip closest to the firewall is way out of place and at the wrong angle. Just pull the cable out and let it hang free for smooth operation.)

You could also install a secondary throttle spring. Better automotive and hardware stores will have springs you can use. This will give your foot a more consistent pedal position feel.

The weather matters because the air just gets more dense (and the problem worse) when it's cold outside - the air is cold to start with, then it gets boosted, and THEN cooled by an even colder-than-normal intercooler. This is incredibly dense air, especially compared to the 6-9 psi most "turbo" cars see.

Meanwhile...

At the exact same time this compressed air is sneaking around the on-it's-way-to-being-closed throttle blade, your clutch is being pressed by your left foot with the intention of having it be timed correctly with the let-up of your gas foot.

Problem is, the timing you have selected for your clutch pedal is based on the percieved release point, which is most often affecting/writing your cranial habit-code when you're putzing around, driving nice and slow and smooth.

The point is that identical clutch timing from a "non-boosting" shift to a "boosting" shift will show huge differences in actual clutch-release times just because there is a huge amount of power breaking that ***** loose in one instance, and in the other, hardly any force at all.

The reason the problem is more pronounced at mid-range RPM is because this is where boost swell is most often coupled with relatively low piston-pumping by the engine's internals. A little bit of leaked-by air at these RPM's will go further to free rev the engine than the same amount of air applied to an engine that is already gobbling just-about that much already. When you shift at nearly redline, your engine is at the far end of operating efficiency, rather than being right in the middle (at ~4k, for instance).

The cumulative point is that you're getting burned by both pedals when boost is involved, and especially in the middle RPM range. The simple (and beautifully CHEAP solution) is to proactively and intently train your shift timing to compensate for the clutch's want to slip sooner, under the load - and to lift your right foot sooner AND higher. If you don't hear that BOV cracking open hard, you're not doing it right.

I've since concluded that this is a very lame byproduct of small displacement/high-boost turbo cars, but one I can live with.

For the folks who are competent and have pursued the problem with the above in mind, and still have a problem, I would look at some cause of unmetered air entering the engine between the throttle blade and intake manifold gasket. There could be something disconnected, cracked, or otherwise letting air in.

Part of why I'm fairly certain that this is about driver error is because so few alternatives exist. Engines don't just rev up "because". They need air.

Also, the guys with the aftermarket EMS's are potentially in their own category. Odd that so many platforms can share the same problem, eh?

Cheers,

Originally Posted by MalibuJack

That sounds like compressor surge actually.. Weird..