Had a similar problem with my 2.8 CRD Euro Voyager. Basically the same engine that is in the Liberty and I get a lot of good info from you guys!
After a long trip my engine started running rough at idle. Under a load it was fine, except for excessive black smoke.
During startup in the morning had a lot of white smoke until it warmed up. Even after warmup it ran rough at idle. The problem was unburned fuel. Huh, why is it not burning all of the fuel? My hunch was that an injector was not fully closing causing smoke and a rough idle.
When these Bosch injectors go bad and don't fully close they will bypass the excess fuel back to the fuel injector pump. They are designed this way to prevent even more fuel from being dumped into the cylinder. In order to do this they are all interconnected via a low pressure return line on the top of the injectors.
It is fairly easy to trouble shoot this. You will have to McGiver some sort of test rig that connects the injector return lines into clear plastic bottles, preferably with graduated markings.
BOTTLE SETUP
This is just a picture I grabbed of the net to show the bottle setup.
Don't expect the bypass amount to be as much as it is here! Mine had only about 1 index unit difference after 2 minutes at idle.
Then start the engine and let it run for approx. a minute or long enough to see a difference. The returned quantity should all be about the same ( I think the book says about 5 percent of one another ). If you find one injector that is definitely returning more than the others, then suspect that it is faulty and not fully closing and therefore bypassing the excess.
New injectors are damned expensive. Here in Germany they run about 550 Euros. I looked on eBay Motors (search Bosch PN 0445110059 ) and found some used ones out of a motor that had only 77,000 km. Payed 75 Euros. Installed it and a new copper gasket washer and this solved my problem. No more smoke during cold start and a smooth idle and no more excess smoke when I punch it on the Autobahn.
Be careful removing the old hardened rubber hoses from the injector t-fittings, which are also hard and brittle. If you break a fitting you'll have to get a replacement from the dealer or Bosch. I have even seen nice aftermarket t-fittings and elbows available in aluminum.
Be sure to use a new copper washer.
Hope this helps.
jb