help with a mark viii

hey all

my brothers 97 mark viii has developed a vibration along with chugging and hesitation. It is rpm related - shakes in neutral and park as well as in gear. the engine surges at idle as if its hunting for the optimum idle speed, and it does that regardless of what gear its in. It seems to smooth out once its above 2000 rpm or so. the CEL is not on.

What do you think?

TIA

alright this thread isnt getting any action. the CEL finally came on, threw a p 0308 code - #8 cyl not firing. im just gonna make a new thread with that in the title in an attempt to get more attention to it. so mods, go ahead and delete this thread i guess. thanks