99 passat auto 1.8t hard slam shift into 1st under specific conditions

Hi everyone,
Just discovered this site a few weeks ago and I’ve learned a lot in the great posts here. So here’s the situation. I have an opportunity to purchase my sister’s passat but of course she’s selling it due to some potentially major problems; my dad and I are pretty handy car mechanics and have the patience though to troubleshoot the car.

Here’s the specs and issue:
1999 Passat 1.8t with auto tiptronic transmission
140,000 miles

History & Problem:
In November 2007, my sister took the car in to the dealer due to hard shifting and no functioning of the tiptronic. The dealership replaced the shifter magnets and changed the transmission fluid (first time). The tiptronic worked again and the dealership reported no excessive metal in the pan but verified the hard shifting and stated on paper that the transmission would need to be replaced sometime soon but gave not specifics other than hard shifting.

In April 2008, the tiptronic went out again and the transmission shifting was apparently difficult again. My sister took it in and according to the paperwork, the following error codes were recorded:
-PO300, PO302 (cylinder misfires)
- brake light switch (can’t remember code)
So no specific trans codes other than the brake light switch. They stopped driving the car at that point due to the shifting.

This month my dad and I looked at it when I was in town. Here’s the driving symptoms:
1. No tiptronic function.
2. Hard shift into 1st gear, but I can make it not happen: If I brake to a stop in the car and then push the gas hard, the shift into first gear is incredibly hard, like a slam into first gear. Once it gets into first gear, every other shift upwards and downwards is completely smooth. So the only symptom is this incredibly hard shift into first – the car will jerk forward even. BUT…I can make it not happend: If I brake to a stop in the car and wait a few seconds, I can hear and feel the car shift into neutral and then if I apply the gas, it is a totally smooth shift into first gear; so it only happens if I stop and then step on the gas hard without giving the trans a few seconds to do whatever it needs to do to be ready to go into first gear smoothly.

Our other troubleshooting has entailed this so far:
1) A mechanic friend has a basic vag-com which we used and we picked up no trans faulty codes other than the brake light switch and the random misfires. We cleared the codes.
2) We bought a liter of transmission fluid from the dealer. We were able to put the whole liter in without the fluid overflowing through the filler hole at all. The driving was the same before and after.

Reading through the posts here on passatworld, we think it could be any of the following:
1. Multifunction switch (yet no tranny error code to indicate this is faulty and the dash lights are totally normal)
2. Torque converter
3. Maybe more trans fluid is needed?? (yet it was supposedly just changed a year ago by the darn dealer….)
4. Something else internal with the tranny which may mean a new tranny is needed?

So I’m basically trying to figure out if the car may need a new tranny, or if there’s only a component of it that I could replace to get it going without this terrible shifting. The tiptronic issue may just be the magnets again.

Thoughts on what may be causing the hard shifting symptoms?
Thanks everyone.