Pinched/Blocked Leader Hose or Bad Motivator?

[Stang70Fastback]

So I'm having an issue with the car where it stumbles under itself when I'm idling, and I've been tracking down possible causes for this problem, but I've run out of options. The issue seems to be related to a noise I hear around where the motivator sits, and it sounds an awful lot like the bearing in the motivator might be going bad, and causing it to stick. I'ts a sort of grinding noise that happens about 30 seconds before the problem occurs. The problem is, if I remove the motivator and try running the car on bypass, the problem persists, so I'm not entirely certain that's the cause of the problem. Then again, I'm not sure if the motivator actually affects engine operation at idle anyway.

 

The other thing that I thought it could be was the leader hose leading to the valve card on the left side of the engine. I don't really have a good way to reach it, and the compression fitting on one end of the hose is so rusted I don't know if I'll be able to remove it. The only reason I think this hose might be my issue is because the same thing happened on my old Engola, but that car ran a different type of coolant which was prone to causing these kinds of issues.

 

Does anyone know if leader hose blockage is a common issue on these vehicles? Or if the motivator could be the source of my problems? I really want to get this resolved because every time this problem happens I have to unplug the core control module in order to reset it or the car won't start again, which is annoying, to say the least, when it's 30 degrees out and raining.