Idle went haywire last night, possibly the o2?

[Johnny B]

So getting off the highway in my 84 4000q, I realize my idle is no longer stable, and is now varying between 800rpm and 1200 rpm (Up then down then up then down then up then down etc etc).. I also noticed a strong odor of fuel at idle that wasnt there before.. Im assuming my o2 bit the dust but wasnt sure if it'd give the idle adjustments on the JT like a dead o2 does on newer cars. insight appreciated!