dubhov

Hi all!

I didn't want to spam ALL the P-car forums looking for help, but I'm about at that point... I posted this on 6speed already, and no one's had a similar issues, only hunches...so I'm hoping someone can help, or at least offer some more ideas.

Here's the post verbatim:

"Has anyone had a problem where, while up-shifting through gears, the engine tachs up a little more after the clutch is disengaged? So:

-Clutch in
-Engine revs a little more
-Next gear

Any ideas? A forum search didn't yield much. A google search hints at either the throttle open/close timing being too slow, or maybe the diverter valve not working right and forcing the leftover boost against the throttle plate. "

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I'm ordering 2 new AP DVs and an F-hose, and I made an attempt at cleaning the throttle body last night. (I'm pretty green, and didn't have the right tools...I do now and will be doing the cleaning this weekend when I get time). I'm leaning towards the DV(s) not releasing as they should, and extra boost forcing the butterfly plate on the TB open...

Kevin

1) What mods does your car have? Stock clutch or?

2) Have you pressurized your intake system?

dubhov

1.) I have a tune (I don't know what kind...didn't ask). No other mods, and stock clutch. I'm less suspicious of the tune because it did this before it as well. It's exacerbated by higher boost, so it did it under high throttle when stock as well; it's just more prevalent now since I'm always on higher boost.

2.) Nope

993c2cab

My bet is stock clutch is slipping. Happened to me after my flash.

dubhov

That was the other (more expensive ) thing I was leaning towards too...I can't fathom how that would cause revs to happen after I've already disengaged the clutch though. Some sort of e-gas issue tied to clutch [dis]engagement?

SSST

It could be as simple as your timing between engaging the clutch and getting your foot off the gas is a little off, and you are still on the throttle a bit when the clutch disengages.

Hard to say without more information, but it would cost nothing to eliminate that as the cause. Just lift your right foot a little earlier.

fly2low

or the dual mass flywheel pulling the rpms higher after clutch engaged, assuming rpms were climbing at point of clutch disengagement

dubhov

I wish it was as simple as this one...I'm 100% off the throttle though. It really messes with your muscle memory when you're expecting the rpms to be lower.

This one intrigues me...what would be the fix to this? Lower the power from the tune? If I go WOT, reach near-redline, then don't shift and let the RPMs drop, I don't see this same extra rev, so you might be onto something...that or the clutch slipping idea suggested earlier.

neanicu

I am not familiar with the 996 TT throttle body. Is it cable driven?
It could be sticky throttle body...it happens in other cars...don't know about the TT...

dubhov

It's drive-by-wire...first thing I'm gonna do is clean the TB (when I get a chance to).

Macster

The tach lags.

My WAG is you come off the throttle and the engine rpms stop rising and in fact should drop (the FW can't increase engine speed) and the tach's reading goes up a bit as it gets the next packet of RPM data over the CAN bus.

In some cars, I have not noticed this in my Turbo or Boxster, but it was very obvious with my '96 Mustang GT, there is a delay in the throttle closing when taking one's foot off the gas pedal.

This is to help emissions (and there may be some other reason but I can't think off hand what it would be) by holding the throttle open/closing a bit slower than it would otherwise.

The Mustang has a very nice overrun sound to it do to this.

powdrhound

I friend of mine had the same, or very similar, issue with his bone stock car after he got a UMW tune. The rpms would just hang there forever after coming off the throttle and pressing in the clutch. It turned out that the tune he got was one set up for a lwfw instead a dmfw. They sent him a dual mass flywheel tune, if I understood him correctly, and that took care of it.

dubhov

I did see some posts from other car forums about how this was included in their OEM setups and how they can get rid of it with a tune. Nothing about it ever happening on any Porsches though...mostly Japanese cars.

If it is tune related, I'll probably find out tomorrow. Going in to my mechanic (also guy who tuned it) and he's going to data-log while we go for a ride. Fingers crossed....thanks for the input guys.

Bates

CincyScott

Ever since I got my car (even before I put the UMW tune in), if you revved the car very hard, you can feel a vibration in the bottom of your foot on the pedal...I don't recall that on my other 996's. Any idea what causes that?

I have the stock clutch and it's relatively new (call it 10k miles).