1.6 Duratec engine. Has headgasket issue but was idling fine. In the course of tracking down the headgasket leak I was disabling cylinder 1 spark plug by disconnecting the wire and using a spare spark plug on it well grounded so as not to stress the coil pack. Car did not like running on three cylinders, then gauges started behaving oddly like the speedometer going full swing and back. Connect back up the cylinder 1 plug and the car won't idle; as soon as i take my foot off the throttle it judders to a stop. I have tried disconnecting the battery negative etc. to reset things but no change. Also there now seems a bit of a lag in response to throttle movements. Definitely won't idle.
Any ideas what's happened and how I can restore idling?

 

Can anyone help with this please? There is no seperate idle control valve; its the model where everything is in the throttle body. The two vacuum hoses coming off are OK, no splits. Is there any way to make it reset?

UPDATE: If I take off one of the two small vacuum hoses from the throttle body to some kind of switch, the car will idle; obviously letting enough air in to keep it idling. But that doesn't really solve the problem does it as it is supposed to be connected to that switch.

Thanks for all your help on this!

I got it sorted by taking off the throttle body and cleaning it with carb cleaner. It was bunged up so that althought the butterfly was partially open, not enough air was getting through. I don't know why this coincided with my spark plug testing; maybe coincidence or maybe the misfiring was causing some blow back of gunk.