I am not sure if your car is actually rough running ,or you are not used to the three cylinder vibration. Feels 'somewhat' (not exactly, but not far off) like a Harley when at very low idle.
Sir, you will need to do some diagnosis before making decisions about the roughness of your car. as MetroMPG said first is a compression test and then I would go to a cylinder bleed test. These engines are a little sensitive in the valve area. Very easy to get one with a burned valve. My experience shows they generally burn # 3 exhaust. ( I've rebuilt 11 heads so far; #1 on 2 heads, #2 on 1 head ,#3 on 8 heads.) I keep valves in stock now just for the metro owners my old boss refers to me.
He thinks I'm crazy too.
If these are good then you need to check you ignition system (you might do this first)it is easier and doesn't require replacement of the plugs. I just replace them any time I have to pull them, They're cheap and a good investment.
A good shop manual is your best tool, and a friend at the local repair shop won't hurt either.
I have "Mitchell On Demand 5.5" myself. Wouldn't trade it for the world. (not true, every man has a price, mine is just realllly high.)
