Volvo Repair: Fuel octane, octane fuel, octane gas

Question
I have a 1983 244 GL wagon (odometer stopped about a year ago at 244,000+ miles). It has always run on 91 octane fuel. My boyfriend offered to put gas in it the other day, as the tank was just about empty. He knows to only use 91 octane fuel, but for some reason he put in 89 (over 1/2 a tank).

The car now runs extremely rough - it hesitates, almost stalls, and sounds terrible (throaty). Could this be from using the lower octane gas? If so, how much damage is it doing to the engine?  

Answer
Sheryl, On the older 240's, unless it was a Turbo Car, 91 was not necessary.  May be coincidental.  No damage will ocurr.  Just need to run it all out and refill.  An airmass meter may have gone bad as well.  I would unplug it and see if it improves.  Its the plug on the silver meter going into the airbox.  If it surges when its unplugged, thats fine.  Now plug it in, If it stalls, then a new meter is needed.  Dont faint.  Last time I checked those things were about $400.  Roger