id do the thermostat. I had problems with getting my car up to temp and keeping it there. The blower motor for my heat worked perfect but it wasnt as hot as it should have been. With that said i did a thermostat and temp sensor (had a little but of corrosion) and it was thumbs up from there. Is the blower blowing with cold air, or not working at all. Also check a fuse if it is not blowing.

 

The shuddering? Do you have ABS?

 

Hi, I had the exact same problem, when I changed tyres and got alignment done it righted itself. Running like a dream now!

Thought u guys mite like this, friend just sent it to me!

http://www.youtube.com/watch?v=fxjMhWgGc58