I'm willing to bet this is all due to vacuum leaks. If our customer chooses to tackle the problem, we usually start by removing the intake manifold and replace all the gaskets including the plenum seals, all the hoses underneath, vacuum lines and all injectors and seals. 90% of the time we end up with a car that runs like new. I just did this to a 380 that was so bad that you couldn't get enough throttle response to make it around the block. Now, at idle, you can't even feel it running. I would spray carb cleaner where the intake mates to the head while the car is running. If you have a significant change in idle this may be your problem. I agree with duxthe1, if it's a fuel problem it can get very expensive and hard to diagnose on the old CIS systems.