Get the head off mate, get it tested. I'd park her up too as you could be causing more damage driving her around.. Bad news I know, I've had a HG go on a BMW recently..
Like above, check the 3 sensors Dabsy mentioned first mate. There are way to test them without getting new ones, but google it as I dont want the blame if you short something out. Good luck
As above mate... But just a question, has it been standing a long time and now only doing very short journeys? Thats just clasping at straws and hoping the HG hasn't gave up...I rekon Dabsy is right though.
Well the last few months I have been on a little personal mission to have the lowest e46, on coilovers, on the road, and I'm still planning on using it as a daily! It's still a work in progress but here are a few teaser pictures.