A common problem on these engines is the idle speed cntroller gets clogged up with dirt.
These are easy to remove (2 8mm bolts). Once you take it off, give it a good wash with brake cleaner spray.
One of the reasons for it being intermmittent is due to the heat from the engine loosening up the dirt in the valve, (only for the issue to retrn when the engine is cold).

Thank fully you may have caught this issue when it was begining to start - Meaning you havent completley wrecked the part.