Rough idle and poor gas milage

[bobsgym]

I have 03 Liberty sport with 3.7. It has a slight rough idle and gets poorish gas milage. any suggestions are to where I should start to look for problems. any help would be great.

 

[ridenby]

I would start with plugs,copper just like came in it,assuming air filter etc have been cared for.

 

[jnaut]

I would start with plugs,copper just like came in it,assuming air filter etc have been cared for.

This.

Check for codes as well. When was your last plug change?

 

[BjBnet]

not sure if this applies to you but you will see a difference when winter gas is "taken off the shelf" this spring
....and it's a liberty, if you are getting good mileage...there's something wrong. lol

 

[LibertyTC]

Gas Mileage!

We need a new icon under smile$..
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[bobsgym]

I bought it a month ago and I was told it had fresh plugs in it. I dismissed the slightly rough idle because I thought it was from sitting for awhile. As for the codes the check engine light does not come on. I was told by my local garage there would be no codes to check if the engine does not come on.

 

[LibertyTC]

I would pull one or two plugs to confirm new plugs in there and correct type & gap. Stock NGK or Autolite's
Going to copy this and paste from another post:
Spark Plugs should also be changed every 30k miles, NGK or Autolite Double Platinum should be used. Here is a how video that gives you an idea how to do your own plugs. It is not that hard, and the jeep will run better/smoother with fresh plugs.
http://www.youtube.com/watch?v=DxsEOCqhHx8
Cleaning the throttle body and IAC (intake air control) is something that should also be done every 30k. http://www.jeepkj.com/forum/showthread.php?t=47972
Replace or clean the PCV valve every 30k is a good idea as well.
I would also consider using Mobil 1 synthetic 5W-30 motor oil and a quality filter like Mobil1 or Purolator. Synthetics flow better in cold to-47 which allows easier starts, with less carbon by products and better cleaning properties to keep the Jeep happy. Most of us use the Mobil 1 synthetic for our engine oil.
May consider a good fuel injector cleaner like Chevron Techron as well.

 

[diyman]

FWIW, other that the PCV valve, there's an inexpensive ( and mostly ignored...) small sponge filter in the airbox...

Change or clean it with some gas, don't know mileage but idle should stabilize. At least it worked for me...

Also, a can of injector cleaner and an 'italian tune-up' sometimes do miracles

 

[bobsgym]

Thanks for all the help. I am going to pull the plugs this weekend weather permitting and see what kind and what shape they are in.