Finding vacuum leaks use carb or throttle body clean. Spray area and if engine RPM's change, you have a vacuum leak at that location. Be sure to spray around the intake manifold and all hoses. This includes the power brake vacuum line and the vacuum lines running back to the gas tank under the car.
IACV is part of the throttle body. In the upper right hand corner of this page is a box that says "Search", use it.
You will find posts about cleaning the IACV, and if I remember right, there are pictures too. This has more to do with idle speed then anything else.
Motor mounts, as vibrologist said, look for cracks in the rubber. Compare pictures of new mounts to the ones you have. Pictures can be found at http://www.rockauto.com
of most any part. The rubber portion of the mounts that are round in shape on the out side, when new, will have the inside hole centered in the rubber. If the inside hole is not centered in the rubber, it has deformed over time. Watch for motor movement when under load as vibrologist suggested. There will always be some movement as that is what the mounts are for but there should not be a lot. You can watch the mounts and see how much they compress under load. If the rubber compresses a lot replace the mount. Also use the "Search" on this board about motor mounts because I have seen posts here in the past about this topic.
This motor does not have balance shafts, which really do not balance anything. Balance shafts are a counter balance of the forces from the pistons and crankshaft movement used on line motors or single cylinder engines. They can help smooth out an engine in some RPM ranges but also add more moving parts that can wear out and take more power from the engine to turn the shaft or shafts.
No harmonic balancer either. Harmonic balancers are typically used to dampen torsional vibrations with in the crankshaft. In most 4 cylinder engines there is not enough crankshaft length or journals where harmonics become a problem for the crankshaft, so a balancer for it is not needed.