Fiat Tipo, fast idle and loss of power at low revs

My daughter has a 1990 Fiat Tipo 1.6 with the early ECU.

It doesn't pull as I would expect in low revs (you need to be doing at
least 50mph for it to be happy in 5th) and it will only idle at around
1200 rpm.

Gut feel says petrol, but I also understand that a weak spark can cause
the same symptoms.

Do the learned people of this newsgroup have any suggestions?

Cheers

Peter