WOW. I am glad this thread has started. Everyone has given great responses and possible problems. I have just recently had the exact same symptoms with my 82 zx turbo. I just filled the tank and when I left the station I gave it WOT into 2nd gear. Now it idles very rough and at cruise it stutters. I still have the same power but it is quite smelly now and it backfired a couple times.
1982 turbo. No cat, EGR pinched off, everything else is pretty much stock. I know I need plugs soon anyway, so here is hoping that is the problem!