I have this problem too - can you remind me which one is the coolant temperature sensor?
How did you test it was faulty? I've always meant to look at my early morning starting 'stumbling' but never have the time..
Does your engine now idle when cold somewhat above the usual 750rpm, whereas it didn't before?
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black