Hego normally doesn't cuase the surging idle. That suggests a blocked Crankcase breather (PSV) valve to me. Its cheap to replace (just fiddly) and is supposed to be changed every 30k miles
Take a look at my web site I have a huge section on idle probs in my information pages
Mad Mole
Visit
Mad Moles Mondeo Madness 2L Zetec, Cams, Stage 2 head, Valve work, Powerflow, Unichip, AEM Ram, K&N, Ecotek, 75mm Lower etc.
192 BHP, Faster than a speeding Duratec!
