Rough Idle when warmed up

[JonH]

Hi, I have 97 EFI Auto Festiva with A/Cond. It's current problem is that when it has reached operating temperature it has a very lumpy idle. When you increase the revs it goes through a very pronounced flat spot before it clears and runs normally. When first started from cold or slightly warm it runs well. Only when it has warmed up does it have the flat spot and lousy idle. We have changed the leads, plugs, disy cap and rotor with little effect. All ideas and suggestions will be greatly appreciated. Thanks,

Jon

[FestYboy]

vac leak...

location would help: go into User CP, select edit details and input location info.

[JonH]

Thanks for the clue - Vacuum. To answer your question, my location is Sydney, Australia.

I was thinking also to check the Ignition Timing. However I can't see how I would get a timing light in to where it is needed. Do you come at it from the top of the engine or from under the car?