Man we seriously need a "How To" section in here !! You can also search in this forum info like this.
If the CE light is not on, it probably does not have any codes stored.
For reading stored codes, without starting Jeep,
Turn Ignition Key..On-Off-On-Off -ON and leave it on. In the spedometer where it shows the digital mileage, it shuould show the stored codes sequentially eg: P0442 is the code #
Otherwise you can obtain an OBDII reader that does many other things including reading pending code as well.
Consider getting a Haynes service manual it will help with servicing your Jeep Liberty.
How many miles on your Jeep & spark plugs? Plugs should be changed every 30-40K miles.
If you change your plugs you will know what a coil pack is.
YouTube - How To Change Spark Plugs 02-07 Jeep Liberty 3.7L
Start a process of elimination: Spark Plugs First. Under hood Label tell spark plug gap and type.
Next try the bottle of Chevron Techron in your fuel. This may help clean the injectors.
Bad plugs or coil packs & TPS sensor tend to throw misfire codes.
Start with the two item and note your old plugs condition and old plug gaps.
If they look worn down and are anything other than tan brown, post back you findings.