I believe 1986 was the first year Mopar used the computer controlled Q-jet. It was used on the Grand Fury and Diplomat police cars and maybe other models. I don't know if that carb was used on the 5th Avenues.

I've wondered if the mixture control valve in one of these computer controlled carbs could be manipulated to make an engine run lean to improve gas mileage? I worked on one of the ex-police cars years back that had the computer controlled carb. That car was running full rich and getting single digit gas mileage. I don't know how an engine would perform if the carb was stuck at full lean. If driveability was acceptable it may get great fuel mileage.