What would cause an engine to shake?

It

The injector pipe is a red herring if the engine's idling and you've not changed the injector it's feeding.

So at the miles you reckon that the injectors should be changed?

I didn't say that. In fact I've no idea what the problem is as such, but as long as the replacement pipe was clean inside it will flow enough fuel for idling even if it's under bore for full throttle running. The fuel flow is basically controlled by the pump and injectors, not the pipes that connect them.