I'm going to just copy-paste some information from easterncatalytic.com here. Apparently double-digit fuel trims are usually indicative of a problem.
From the website:
Diagnosing with Fuel Trims
Fuel trims can help you zero in on the problem, especially when there are no other trouble codes present. Knowing whether a vehicle is running too rich or too lean will help narrow down your diagnosis. Fuel trims that differ greatly from one cylinder bank to the other will also point you in the right direction. Always evaluate fuel trims at idle and at 2500 RPM.
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.
Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter.
Diagnostic Tip:
For a suspected vacuum leak, note the fuel trims at idle and increase engine speed to 2500 RPM and hold. If the STFT immediately decreases and moves to acceptable levels and the LTFT slowly starts to come back down, you have a vacuum leak. After the repair, reset the KAM and start the vehicle. Monitor the fuel trims to make sure they are within the normal ranges. It could take up to 10 miles of driving for an accurate LTFT reading.
You can read more about fuel trims here:
What are fuel trims all about?
And from O'Reilly Auto, on misfires:
There are four main causes of engine misfires - a loss of spark, an unbalanced air/fuel ratio, a faulty fuel injector and a loss of compression. The loss of a spark could mean that the spark plug needs to be replaced, which is a relatively simple process. It may also be caused by a faulty spark plug wires. In either case, if the spark plugs or wires are failing in one cylinder, they will need to be replaced. When one spark plug or wire goes bad, there's a good chance the others are not far behind. It is a good idea to replace all of the others when replacing one of these components.
If the mixture of fuel and air is too lean - meaning there is more air than fuel - then it will be unable to ignite, even if the spark plugs are working. There is also a possibility that the mixture is too rich - too much gasoline - even though this tends to be far less common than a lean mixture. A gasoline-heavy ratio of air and fuel can occur if the fuel injector leaks, but this tends to occur in all cylinders, not just one, if it happens.
An improper mixture can be caused by leaks in the fuel lines, a weak fuel pump or a faulty fuel injector. It is important to check the fuel injector on the problematic cylinder. It should spray a fine mist of fuel, but if there are drips, it may indicate that it is clogged, dirty or otherwise damaged.
Low compression can also contribute to engine misfires. Pressure in the combustion chamber is just as important to a healthy cylinder as the fuel mixture and the spark that ignites it. If a chamber is losing compression, it means that the gasoline and air are leaving the cylinder before they can be ignited. This can be caused by leaky vacuum hoses, a busted exhaust valve or a blown head gasket. When two adjacent cylinders are misfiring, chances are that the gasket between them is cracked or damaged.