It's no problem to disconnect the fuel injector connectors while the car is running. If you find that disconnecting one of them makes no difference in the way the car is running, then that's the cylinder with the problem. You may even find corrosion inside one of the connectors or on the terminals on the injectors (such corrosion has also been known to cause a problem).

With respect to a possibly leaking intake manifold gasket, my lesson learned from my last experience is just to go ahead and replace it if I suspect it for any reason. It's just 8 nuts and it's not a problem-gasket that you have to scrape off. You don't even have to disconnect anything from the manifold... just undo the 8 nuts and pull the manifold back the couple inches you need to get the old one out and new one on. In my opinion the gasket is easier to swap out than to try to search for leaks in other ways. Gasket is $3 from fcpgroton

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Matt L. -- Cary, NC -- '91 740 wagon