tiptronic transmission shift normal when car is cold,when warmed up 3rd gear slipps
 

HI all,

i have a problem with my 99 boxster,it shifts normal when the car sits for a while and when i drive for about 5 kms and up the 3rd gear wont engage,it slipps
and again when it sits for a half hour it shifts normal

please advise if you have any suggestions

Sounds like
 

heat related and since the trans is cooled by the fluid inside and by a center radiator, I'd look at the fluid level.

When did you last change the fluid and filter? Lifetime really isn't. Also if you have a Durametric you could check for fault codes in the trans. ED

I just did a TIP service on my 2000 S. Fluid was very dirty and I believe it was a good liter low, maybe more. Shifts a lot better now. The TIP electronic plug coming out of the trans has a connector to the harness...someone else had a problem and found dirt and grime had made a connection weak...cleaning solved his problem. :cheers: