2002 Nissan X-Trail • 80,000 miles

My nissan x-trail, when started cold or when it has been driven a couple of hours ago, it idles rough on start up, then goes away shortly after, even when you rev it a little.
I had the throttle body cleaned and the injectors serviced and new spark plugs put in. Even with the old spark plugs it is doing the same. Before the service it idled rough, and now with the service done it still idles rough on start up. Also I'm topping up the coolant in the resevoir on a weekly basis.
What could this all mean?
Thank you for your help.
October 28, 2012.

Topping up the coolant could mean either a leak in the system or you have a bad head gasket. If the reservoir is depleting as well, that is due to a leak in the system. If reservoir is increasing in level, you most probably have a bad head gasket.

A bad gasket is consistent with the symptoms as per the erratic idling during startup.

Hae a pressure test performed.

Oct 28, 2012.