I just had my intake gasket changed on my 99 Monte Carlo for the same thing. My cousin is a mechanic and has changed the same gasket on several cars with the 3.1 engine. The gasket is about $60 - $75 plus labor.
you have a coolant leak
Intake manifold at top of engine?
It can if it is leaking coolant into engine or out side of engine.
Need to check the 4 corners on the intake manifold. It is common for the intake to leak engine coolant.
It is on the intake manifold near the thermostat.
Yes they do at the intake manifold.
Don't generally see an intake manifold go bad, it is usually the intake manifold gaskets that go bad in which case you may see engine coolant leaking out in the corners or worse case leaking into the engine and mixing with the oil.
Next to the water neck on the front of the intake manifold.
Intake manifold gasket
It is on the intake manifold near the thermostat housing.
It is the sealing part that seals the intake manifold to the cylinder heads and to the top of the engine block. The intake manifold is the part that distributes the air to the cylinders. It also can house the thermostat, the injectors, the throttle plate. An intake gasket could leak coolant, engine oil, or engine vaccuum.
The coolant drain plug on a Nissan Micra engine block is on the upper part of the block. It is under the intake manifold.