Sounds like a blocked PCV valve
Take a look at my web site below. Huge section on idle problems in the information pages
Mad Mole
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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!
