My daughter has a 2004 Ford Ka. It has developed an intermittent fault whereby it will often over-rev when idling or rev in "pulses" as if someone is fanning the throttle. It has now also started running off at lights/junctions etc. I have taken it to two local garages who hooked it up to a computer but could find nothing wrong. They also checked for air leaks and drew a blank there too. They both suggested I took it to a Ford main dealer. Would this be a sensible option for such an old car and are they likely to have any more success diagnosing the fault than an independent garage?