Regulatori

So today I was driving and noticed the car started revving up a bit after every shift even though my foot was off the accelerator. It did it in first a little but then was more pronounced in 3rd..and after it did the little 2-400rpm blip, the rev counter needle went down slower than normal. Kind of like that noise if you go to shift and you accidentally rest your foot on the accelerator before letting out the clutch. Just a bit of over-rev.

First I checked for the obvious like somehow the floor mat was wedged against the accelerator but that wasn't the case. I'm going to check the linkage in a bit. The clutch itself feels fine and I'm not feeling any slip.

Just seeing if anyone had a quick guess before I start checking things out.

Regulatori

No one?
We've had snow all this week so I haven't been able to mess with stuff.

I'll try to better explain it.

When I press the clutch in while shifting, the revs continually rise for a second even though my foot is totally off the gas/accelerator. It's not that bad in 1-2 but it's more noticeable in 2-3 or 3-4. It's the same sound as if you accidentally rest your foot on the accelerator while shifting....you just get a bit of rpm rise between shifts. The revs don't fall as fast either and just seem to hang for a second like I installed some super heavy flywheel.

Sometimes it's embarrassing because I'll be driving around in slower traffic and the sounds coming from the car make it as if I've never driven a manual car before. haha

Could this be a clutch issue? The clutch grabs fine in all gears and doesn't slip....it is the original clutch though (1993) but the car only has 70K total miles. The original owner was an enthusiasts with a lot of older sports cars...the guy knew how to drive a clutch and not slip it/burn it out so I know the clutch has a lot of life left in it.

koenig_roland

I´ve the same problem on my C4.
I expect it´s a "Leerlaufsteller" problem. I don´t know the englisch word, but i mean the valve that keeps the idle continuous.

I think, cleaning this valve could solve the issue...

Rocket Rob

The air cooled VW bugs had this problem if the clutch cable and throttle cables got twisted in the tunnel but the 964's clutch is hydraulic so that can't be the cause. Have you take a close look at the foot pedal assembly? I would look for anything linking the clutch movement to the gas pedal. I can't imagine what would cause this on the engine/tranny end of the car unless its a poorly adjusted throttle cable. How long had this been happening?

sml

I had the exact opposite problem! So I was thinking of suggesting the same. When changing gear, the revs seems to drop sharply that gave me a feeling of needing to rush the gear change. I just thought it was a Porsche 964 performance thing. But I ended up cleaning the ISV to try to resolve the common idle sub-dipping issue, but interestingly the ISV clean resolved the slightly sharp idle drop between gear changes. I agree with a comment that someone posted about cleaning the ISV every 2000 miles or so. My ISV looked perfect although i couldn't 'rattle' the valve in my hand suggesting a problem. Then I connected a 9v battery and then some dirt was revealed on a small section of that moving section of the valve. Cleaned up until I could get an easy rattle, then installed

altarchsa

sounds like the throttle cable adjustment to me. Anyway, it would be an easy thing to check it before you pull off the idle control solenoid to clean it. Do a search for both as they've been covered here before.

Regulatori

Just an update. Ended up cleaning my ISV (the idle valve) and it was nasty inside. Now my idle is a lot smoother and the throttle blip is eliminated. Car runs perfect.
Thanks

Regulatori

Well the problem is back and after really getting a chance to drive the car (better weather) and experimenting, I've noticed this...

-The throttle rise has NOTHING to do with clutch engagement but totally dependent on throttle.

-If I'm at 100% throttle and lift my foot off the gas, the car keeps accelerating for a second and then the falls like normal.

-It happens if I give the car full throttle in 2nd gear at 6000rpm or full throttle in 4th gear at 2000rpm...I still get that same extra throttle rise.

-It doesn't happen if I give the car 3/4 throttle....ONLY 100%.

-It's that same feeling when you're in cruise control and the car briefly accelerates to match the set speed.

-I'm sure it's not the clutch....I can drop the car in 5th at 1500rpm and the car will still pull with no slipping.


I'm thinking it could be a throttle cable, cruise cable, or some type of throttle sensor. Is there a way to check that the throttle/cruise cable are not too tight/loose? I went through Adrian's book and couldn't find any info.

Laker

have someone sit in the car (not running) and press the gas pedal 3/4 down and have them tell you when they release. Note how fast the accelerator cable/mechanism snaps back. Repeat with the pedal all the way down. If you notice a slower snap back to the resting/idle position, there is your issue as the cable is getting snagged when doing WOT.

ian89C4

+1 for a possible snag somewhere along the line. The throttle cable can by pulled in its entirety with the engine in the car if ends up being something wrong with the cable itself.