Hot start issues are a common problem on K(E)-Jetronic units and easy to solve.

But in your case it was the relay, funny it's not running properly now. Maybe you had a short circuit while you parked the car that fried the relay and maybe the Jetronic box, too.

Have you checked the spark plugs?
Does it not run at all? Or maybe just unable to idle?

EDIT: What else did you do? The K(E)-Jetronic is VERY sensitive when it comes to air leaks. When you disconnected a little hose somewhere the car might start but will cut out immediately.