Mine is a nice car with 75,000 miles and in Florida I didn't have a problem but touring in the North Carolina mountains it would detonate badly even on 93 octane.
When I got home I fitted 2 pieces of radiator hose to the airbox inlets and took them to the front side of the radiator.
I then put a piece foam rubber on the top of the radiator and shut the hood.
The car now breathes cool air that has not been heated by the radiator and the problem has gone away.

 

@nofking

Sounds good. Any chance of a picture or two?

I have been messing around with my air intakes and was about to embark on the major project of cutting holes behind the headlights and routing the intakes through there to the front of the car, but your idea sounds a lot easier....

 

there are other factors that may no necessarily correlate. For sure the air in the mountains are thinner, which could add to this, but "touring" could mean driving the car long enough to expand the fuel and cause shotty flow.
Not to mention if you are talking about driving in a different area, especially a rural one,the gas can be of a different quality...

If its fixed though, all the power to ya

 

On my 90 there is a connector on the L/H firewall that has a jumper wire that I believe is just for this situation. It will change the timing for lower octane fuel.

 

This jumper is on all Marelli cars. Removing the jumper puts the car in a map for lower octane fuel.

 

where would that connector be ?