I had the same issue with my 99 plate IS200. It's the calibers causing binding on the disc. (that's why your discs are getting red hot). The pistons are sticking causing the pads to be in contact with the disc at all times even when you're not braking. You need to replace both as soon as possible and that will stop the juddering. I would avoid driving the car too far as the discs will just get hotter and hotter, this may cause a brake failure. I bought a pair of reconditioned on ebay and sent the old ones back to them in order to get a deposit back. Think I paid around £100 and its an easy job too.
