worn CIS injectors
Often the CIS injector seats wear unevenly with age and will start to 'leak' on shutdown, even though they had a good spray pattern., This leads to hard hot starts(flooded cylinders), and worse, lots of gas dribbling into the affected cylinder.
Sometimes the leaking is due to trash (gum ) on the seat and can be cleaned with a bench flush with strong solvent. these things open and close many times a second a idle (buzzing), and do eventually wear.
I would recomenf replacing all the injectors and all the rubber, including all the vacuum lines. It gets hard with age and you WILL have vacuum leaks, if not now, for sure when you remove them.
A good smooth slow idle (500RPM) results only with good injectors and no air leaks.
Another source of 'flooding /gas smell' can be the fuel distributor diaphraghm, and replacement is only alternative. If, on shutting down th eengine, removing the air cleaner, and pushing down on the air plate you see liquid fuel in the manifold, the disrtibutor is leaking.