The first thing to do is to change the plugs.
Preferably for something better than the ones originally fitted by Fiat.
You can buy a set of 4 NGK DCPR7EIX iridium plugs off the internet for less than £30 & they'll perform better than new OEM plugs for at least 40,000 miles
.
Second thing to check is the battery - if it's still on the original, it'll be well past its best by now & decent replacements for the non - S/S 1.2's are only about £50 or so.
Third thing is to run a couple of tankfuls of premium unleaded through it - premium fuels usually have a better detergent pack & it'll help clear any accumulated crud from the intake system.