-The crankcase ventilation sucks.
If you are using any oil above 5 W 40 you are sucking oil into your engine and fouling MAP sensor and EGR valve.
0W40 or 5W40 is recommended.
-service intervals do not recommend cleaning MAF and MAP sensors. These two sensors determine if your engine is going to run smoothly or throw codes.
You need to remove and clean them every 15K miles.
-a good clean air filter helps a huge amount.
Adding a mann and hummel provent 200 is a must have!

 

I'll just stay away from the JEEP LIBERTY

 

No, the engine, when dismantled of the green tree hugging items, is okay and mileage is also pretty good.
It is an accepted car in europe.