Hello! I’ve followed this forum for a while, but this is my first post. I have two questions for the tiptronically knowledgeable concerning the (mis)behavior of my Tiptronic-S four-speed transmission in the “manual” mode. 1997 Carrera coupe (US), 31,000 miles.

First, when accelerating in first gear I find that the transmission will shift itself to second gear at 5,500 rpms. From all I’ve read in the “archives”, the rev. limiter is around 6,800 rpm. Second and third gears will allow me to reach the 6,800 rpm limit. Is this lower first gear “limit” within the normal parameters of the transmission, or is this a malfunction?

Secondly, three times in the past few days (but never before) I have experienced the transmission—in Manual mode—shifting itself up a gear under “normal” driving conditions:

first time: in second gear at 35 mph / 3,000 rpms steady speed for about a minute (transmission oil still “cool”), the car suddenly shifts into third.

second time: situation nearly the same as the first, except now the transmission oil should be properly warmed up.

third time: on the highway in third gear at 65 mph / 3,500 rpms, having traveled at this speed for several minutes, the transmission suddenly slips into fourth gear (vehicle having been driven for about 30 minutes before this incident, so the transmission is at “operating temperature”).

I can safely say that my hand did not accidentally bump the steering wheel shifter buttons in any of these three cases. I could find no other reference to this when I searched the archives. Just before I noted this behavior, the transmission was checked by an independent shop well-praised on this board. Its function was normal, and the condition of its oil was considered good.

Three incidents in the past 1,000 miles are not overwhelming, but I am wondering if this is a harbinger of impending failure. Any advice or thoughts gladly welcomed!

Thanks--Jonathan

 

Thats very strange.
Ive never had the gear automatically shift up in manual mode. Down but not up

 

Hmmm. I am on my second Tip car, and have never experienced what you describe. One thought is that weird things can happen when auto trans fluid gets the tiniest bit of contamination, and/or when the fluid is changed after years of inattention (often the same thing, as crud is dislodged by the fluid change). I change the tip fluid every year or two to avoid this.

It could also be some gremlin in the transmission control module. This unit must have some adaptive or learning feature, as in full auto mode it will use one of 5 different shift maps depending on how you have been driving, so maybe a free and quick fix to try would be to disconnect the battery for a while, thus clearing its memory (and perhapds the bad habit as well?). Just a thought, those with more knowledge should chime in and tell me if this makes any sense. For example, I don't know whether it learns only each time the car is turned on, or whether it stores the info over the long haul. I always drive in manual mode so I just don't notice....

I'll leave you with a happy thought: Bruce Anderson stated in Pano last year that Porsche tells him that the original 4-speed tiptronic trans (as in your car) is about the most trouble free transmission they have offered. My mechanic says basically the same thing. So, whatever your problem is, there is no reason to assume the worst. Good luck and let us know of any developments.

 

Doesn't sound normal. Could be a short in the steering wheel tiptronic buttons causing it to shift up.

 

Jonathan,

im actually facing somewhat the same problem. In auto mode, the car shifts gears quite fast which neva happened before. by 60km/h its in the 4th gear..when stepped on, it will be in sports mode for 10-15 secs then back to normal.

 

Its ALIVE!!! <img border="0" alt="[icon501]" title="" src="graemlins/icon501.gif" />

 

Sounds more electronic than oil related. Maybe need to check the tiptronic controller under the seat or, as David suggests, the wiring in the buttons on the wheel.

 

Thanks for the responses. It seems then that the two symptoms may be unrelated. I would guess that the first gear upshift at 5,500 rpms may be a "glitch" in the transmission control unit (something that could be reprogrammed out?), whilst the random, infrequent upshifts could either be a short or a control unit problem as well.

Seve - my problems are different than yours in that this is all occurring for me in the "manual" setting. However our problems may have the same, root cause (transmission control unit?).

Problem-solving-wise the "bad" part is the infrequency of this behavior, so it may take a long time to isolate and diagnose the random problem. The 5,500 shift is of course quite repeatable , so that should be the first thing to approach:

step one - disconnect battery overnight and see if that resets the transmission memory sufficiently to allow rpms higher that 5,500 in first gear.

step two - check connections to the tiptronic control unit ('tcu').

step three - swap out 'tcu' to see if it makes a difference (must find local donor, unless they are inexpensive, which I rather doubt!).

perhaps solving this one will eradicate the other (a fellow can hope). If someone can suggest a different approach or test, please let me know.

Thanks again. --Jonathan

 

Re the 5500 rpm 1st shift - is this a new phenomenon, or only just noticed. My 964 shifts earlier from 1st to 2nd, than other gears, at abot 5800 rpm - I think it may be designed this way, maybe to make best use of torque curve???

 

Jonathan,

thanks for your help, im gonna try some of your tips tommorow..