Out of nowhere my 3.5 disco has started running very rough "chug chug chug"

Its a bit intermittent- occasionally it will smooth out and run nicely but switch off and on again and its back!

Checked all the hoses/leads etc- nothing is obviously missing or falling off. Stepper/throttle pot were changed a month ago to cure idle prob- ran fine until now.

Check igntion timing, could be the dizzy at fault.

only say it because mine mysteriously went out one day, after i had just driven it on the motorway for an hour...

as above or an airleak, I had the same when my vac hoses had split