bmw 318is, cutting out.

hi, i have a 1990 e30 318 iS, today i was driving up the m6 doing about 80, on a warm sunny day, i could then feel the car judderin back and forth slightly it then got progressively worse, i made it to the services, and as soon as i put the clutch in, the engine died, so i had to free wheel into a parking space.  I then opened the bonnet and just let it cool down for around 30 mins under some shade. I started it up, it seemed fine,  i only had a further few miles till home, but it was still juddering.  If anybody could suggest a reason for this and a possible fix for it, i would be very grateful, cheers.