Help! Where has my power gone?!?!

['98 2.5]

Hi, wonder if anyone can help with this problem. I have a Boxster 2.5, 1998 year. I haven't used the car for a week and went to start it today and the battery was totally flat, not even any power to light the dash up. This didn't surprise me too much, as i knew the battery was a bit weak anyway. Luckily the car was indoors with its top down and unlocked so no problem getting into the car.

I connected jump leads to the car and onto a good battery in my workshop and the car started up just fine. However, when i then took it out for a drive, it was a bit jerky at higher revs, and no power at the top end of the rev range. It feels like the variable valve timing is not operating and so is very flat and lacking power at the top end of the rev range.

Now i know some cars have 'limp' modes and i wondered if something like this had kicked in as a result of the flat battery and the jump start. When i got home the battery had enough charge in it to restart ok. I disconnected it, waited a couple of minutes and reconnected, started up and went for a drive and it seemed the same still.

Now it could just be total coincidence that the VVT has packed up on its own and nothing to do with the battery problem, but has anybody out there got any advice/clues/suggestions etc. This car is quite new to me so i don't know it that well yet. Does it have fixed throttle maps, or ones that 'learn' etc??

Any help or comments much appreciated.......

Jonathan