1994 Ford Explorer 1994 Explorer Rough Engine Idle While Co

My daughter's 94 Explorer has a very rough idle when the engine is cold. The engine seems to shudder and reminds me of a vacuum loss problem that I fixed due to a split vaccum hose. This happens only when the car is cold and idling at a stop but when the moving and cold, the shudder is not present. When the engine warms up to normal operating temperature the rough idle is completely gone, even at idle.

I don't see or hear any vacuum leaks. I just took it to a mechanic and it was idling rough when I got there and smoothed out because the car's engine reached operating temperature as he was looking at it. Even though the car was no longer idling rough, the mechanic told me that I had a bad intake manifold gasket. I am not sure how he can to this conclusion as all he did was to spray carburator cleaner along the intake manifold perimeter. If the gasket was leaking, wouldn't it always idle rough regardless of engine temperature? What do you think may be the root cause of the rough engine idle only when the car is not at its normal perating engine temperature?