Engine over revving

My Mk3 Facelift Ghia X is coming up 6 years old and has been so reliable. That was until recently. I noticed when I changed gear, or travelled slowly in traffic, the engine revs would climb up to about 3000 the minute the load was off the engine, only to fall when I braked and the car came to a stop. I initially thought it was the idle control valve and replaced it with no effect. I'm lucky I have Tremona garage just a few miles away, and Richard is a genius. It turned out to be the Crankcase breather hose under the inlet manifold. Richard has dexterous hands and fingers and was able to replace it without removing the inlet manifold. Job done and my Ghia X is running sweet again.