It could be (a) misfiring cylinder(s). Check the condition of your plugs and wires. Also, check if your engine mounts are not worn.
CHECK WIRE
The Ignition Coil is the one that cause misfire or Spark Plugs
lacking of oil to the cylinder possibly, distributers can also be a factor...... also dont forget to check the simple things such as spark plugs or any loose wire connections
Auto Zone will check your computer codes for FREE... Most likely you have bad spark plugs or bad coil packs.
Check spark plugs, plug wires, do a compression test
Check spark plugs and wires Do a compression test
check spark plugs and coil pack
When you replaced the plugs, did you check the compression? Did any of the plugs look different than the others? Low compression in one cylinder can cause misfiring. But then, so can a faulty distributor cap.
2008 malibu 3.6 L code says PO302 misfiring Misfiring in number 2 cylinder. Could be an ignition problem with a bad spark plug or spark plug wire. Could also be a bad fuel injector. Could also be a mechanical problem such as a bad valve. Start with new plugs and wires.
check the coil pack
Check the spark plug wires and spark plugs. You might have to test coils too.