Idle

What is the idle in Neutral, Park and Drive? If you have the idle set too low, it can cause the engine to "shimmy" or feel as if it's running rough.

Compare your idle speed with the factory specs - you may just need to raise it a bit.

Remember, this engine has only four cylinders so if one is less than

You've done the ignition side, now it's time to look at the fuel delivery and air / fuel ratio.

Have you tried some fuel injector cleaner in the fuel?

Fuel injectors can be professionally cleaned.

Check for a small vacuum leak - hose connected to the intake manifold or the gaskets between the intake manifold and cylinder head.

Don't forget to consider the engine mounts. If the engine is ok (e.g. revs fine in neutral) but gives you a slight vibration when you put it in gear then the mounts (which are fluid filled and leak over time) might be the cause.

Josh