How can I cure the over revving on my 1994 Mondeo?

Its been over revving for about 12 months. I have spent £270 on having the EGR valve replaced, and also the idle control valve and throttle body cleaned. Two different garages came up with the two solutions

However it still continues and today it stalled. A friend mentioned the air control valve unit in the filter system leading over the carb unit may be faulty, and I am wondering if this could be the last option. When the intermittant over revving is not there, the car goes well, and I need to keep it on the road until I am 65 in two years time. Car has been well looked after by me and has only done 83k to date. model 1.6 LX. ha s always been serviced every year irrespective of the mileage done in each year. We both think the car is confortable, and we would like to keep it going for another couple of years before we change it