I have a 90 corvette that sits more than now than it use to that started idling
rough. once you gave it some gas didn't seem to be any problems . I had three
injectors that were not working at all. they make a tool now my buddy has one
all you do is have the thing running and point it to each injector and it will tell you if its working. He told me need to drive it to keep things working.
good luck