HELP! Au XR6 manual stalls on ldle

[sickxr]

This morning i went to start my car and my battery died. It was the factory one so i didnt think much of it and just replaced it. Tonight when i got it going again it wouldnt idle without stalling. I thought it may have been some crappy fuel so i filled it up with a tank of BP ulimate. After driving around for around 10mins it still does it. When i turn the AirCon off it wont stall but it will drop down to around 500rpm and then back up to 900rpm and back down again.

It is a AU2 XR6 Manual with 65k on the clock. Any ideas would be great, i guess the next thing would be to change the fuel filter? Or is it something with the computer?

Thanks
Chris