I have a 91 camaro 305 tbi that won't fire up

I checked the spark by putting a screwdriver in the plug wire and holding it roughly half an inch from a ground and the spark bridged the gap. How would I go about testing the rest of those things? Also is that adj effective way to test the spark? It did this out of no where, it was running and then just started doing this. When it was running it would fall on it's face when given a little throttle but only responded well when given a lot of throttle, if that's helpful in any way.

The other thought besides a fuel leak in the engine from the injection system or a lack of air flow to the intake would be an exhaust restriction. If the engine can't breathe, it won't run.