Hello,
I have a 968 tiptronic which was abandoned by the previous owner after an attempted manual swap. I reinstalled the Tiptronic transmission and the issue is it goes into limp mode (stuck in gear, when car is restarted it resorts to second) after 10-20 minutes of driving. This usually happens above 50kmh in 3rd or 4th gear. Before failing, both the automatic and manual modes shift smoothly. One thing to note is the car never shifts down to 1st gear at a stop, but rather uses 2nd. I am unsure if this is by design or an error. I have been chasing this issue for a while now and here are the fixes I have tried:
Alternator- make sure it is producing enough voltage. In my case it was producing ~11.5V before and after adjusting the regulator it jumped to ~13.5.
Transmission connectors- cleaned from any debris or corrosion.
Transmission fluid- flushed and filled with 7L of Dexron 3.
Test Transmission Solenoid valves- All work, but upper most one has a fainter clicking sound.
Fuses and relays- no fuses blown and tried multiple relays for the automatic transmission relay. (G20)
Checked Transmission Control Unit- no visible issues but a deeper inspection may be necessary.
So far none of these have fixed the issue, which I believe is electrical rather than mechanical. I also do not have a Porsche System Tester to check any error codes.
Next steps maybe a dealer inspection, new control unit, new lateral position sensor, or a new transmission.
Any suggestions or experience on the issue?

 

After reading through your list of troubles I only recognize one thing. These cars do not shift down to 1st at a stop sign or just starting off typically. Although its probably unlikely I would be happy to send you a used (not proven) tip computer from a tiptronic part out car if you want to pay the shipping back and forth for your testing purposes. Check your grounds carefully, I suspect the ground post in the hatch/rear tail light area as far as Tip ECU ground issues are concerned with the harness that goes back there. Perhaps discuss a little more about how much and what items were dis-mantled before you took over.

 

Car was actually an attempted turbo and manual swap. Engine side, the cylinder head, exhaust, headers, timings gears, alternator, water pump, and relating sensors/wires were all removed. Transmission side, the gear shifter assembly and entire tiptronic transmission was removed. I took the opportunity to rebuild most of the engine besides the piston rings and bearings. I also replaced the damper plate with a new one. I replaced the transmission filter and checked the solenoids before putting the transmission back in.
I will check the grounds and I appreciate your offer for the control unit.

 

You indicated that you filled with 7L of transmission fluid. I do not know the capacities but do know there is a very specific way to check the level in the owners manual/work shop manual that I think has to do with checking while warm and in neutral. There are two types of fluid, one is Dexron II ATF type for the automatic transmission and on the passenger side there is a place for the differential gear oil of typical gear oil (check this spec). Here is a pic from the owners manual on how to test the ATF fluid level. IIRC correctly the stuff expands when heated or at operating temp.

 

Good and bad news:
car ran fine for about 100 miles/160kms but then the tip light came on again when idling in my driveway. Checked oil and removed a little (at Max mark on the reservoir while at operating temp.) and then ran fine again for maybe 40miles/60kms and then tip light came on again while reversing(low Revs again). Took some more oil out until it was at the 80° C mark (midway through max and min) and then drove fine maybe 10 miles and the light came on while idling again.
I suspect the issue maybe with the engine mounts as they are worn down and there is excess vibration, causing a sensor to potentially trip out. Tiptronic engine mounts are special and more expensive than manual with no aftermarket support as well. I will try to find a pair and bench the car till then.

 

Sounds like a good plan.
I had no idea that the Tiptronic engine mounts would be different, why??
I assume the gearbox is still in the rear? Excuse my ignorance, I have a coupe.
Still 50-50?

-Yogii
AKA 968 Novice

 

Gearbox is still in the rear. The tiptronic engine mounts are heavier duty for the heavier transmission even though they look identical to manual ones. I believe this is done through different hydraulic fluid.

 

Just to be sure, the instructions in the manual about doing the level checks while the car is idling, in neutral, are important, since there will be a good amount of fluid that will be in the torque converter. Apologies if that was clear to you, I didn't catch that from your update, and it's a sort of critical distinction for the oil level assessment.

Cheers