When my coil pack went the idle sounded like a tractor, the engine moved like it had a bad mount and at highway speeds it shimmied and shuddered badly.
Went to Meineke, got a new coil put on, new OEM plugs & OEM wires and problem went away.
I guess it depends on how your coil is dying determines how crappy it runs.
There is a diagnostic to test the coil, the dealer did mine, however...
If it's never been changed I'd bet that's it.
