Fiat Panda engine cutting out when slowing down

I bought my 10 plate Fiat Panda Active 1.1 nearly a year ago.It has done 90800 miles.I have covered around 7000 of those myself.Around 6,7 months ago,I noticed that when I slowed down,the engine would cut out.It restarted either on the key or by letting the clutch out,effectively bump starting it.I had the spark plugs replaced, but it still does the same thing.Sometimes I can go for a week or 2 without any issues.Other times, it cuts out nearly every time I slow down.I use the car 5 days a week for work which is a 30 mile round trip.Any suggestions please?.
also,I have just spent over £700 on the car in 5 weeks.I had a steel hose replaced after it corroded, and the water went boiling high and dried up. The same thing was still happening, water drying up, temp gauge going over the top.I took it to a mechanic who diagnosed the fan was not cutting in, but was working,so a rewire was needed at a cost of £195.00.The heating wasn't working,after 2 days and just blew cold air.I took back it to the same mechanic who charged me £180.00 saying it was the air flaps,(whatever they are).The heating was then superb whilst driving the car the 4 miles home.However, using it today for a 40+mile trip, and half way home, the heating was non existant again.Seems like the mechanic is overcharging me for work that necessarily doesn't need doing, or hasn't even been done.
Anyway,my main concern now is getting this cutting out problem sorted, as long as it isn't an expensive job.I am now about £300 more than what the car cost me to buy.