My Villager has a slight rough idle like a blup-blup sound at the exhaust and a slight engine shake but smooths out when AC is engaged. Runs great with AC on. Any ideas?

 

Well, I've only just bought a Villager, but I have a Maxima, and I
should think the Villager has a similar IAC (Idle Auto Control) valve.
These valves get gummed up causing the symptoms you describe. Remove
the IAC and clean it. The reason it runs better with the A/C on, is
that you're loading the engine, causing the idle control to move
accordingly to supply extra power, thus straightening out the idle at
the same time.

You should also clean the throttle body using carb cleaner.