How about the plug wires? If plug wires don't fix it I'd bet it's the injectors.
Engine misfires. P0300 corresponds to misfires that are random among all cylinders, whereas P0301-P0306 correspond to specific cylinders. I'm not an expert, but other posts I have read seem to suggest that because you are getting misfires across more than one cylinder, it's probably something like your ignition coil, distributor, etc. !
The distributor cap of an ignition system is one possible cause of many for misfires. Other possible sources to investigate are the distributors cap and gears. The flow chart of diagnosing misfires also include the coil, capacitor (if applicable), ignition wires and the spark plugs.
2.2 or 3.5 engine info needed along with codes and which 2 cylinders are misfiring.
Ignition misfires and "sputtering" can be caused by any number of system failures such as air/fuel, ignition and even emissions/exhaust. A failing ignition coil, control module, plug wire and plug are often components that should be examined when diagnosing such misfires.
Misfire Answer Faulty: spark plug, spark plug wire, ignition coil, ignition module, fuel injector are the most common. Coolant leaking into a cylinder is another. Internal engine problems such as burnt valve, broken valve spring, bent push rod, worn rings
Chek out the ignition coils, the wires and the spark plugs..
Wet/damp/faulty ignition wires, contaminated fuel (water), worn out spark plugs.
P0300 is for random engine misfire p0301 and p0305 are misfires on cylinders # 1 and #5 www.lextechautomotivellc.com
P0305 and P0306 indicates that cylinder number 6 is experiencing misfires. A misfire occurs when an insufficient amount of fuel is burning in a cylinder. A misfire from one or more cylinders can be caused by many reasons from a faulty ignition system, fuel system, or internal engine failure
If you are certain the wires are connected to the proper spot on the coil pack then it is likely the coil pack is bad. This is a sonewhat common problem not only on these engines but on very many across many manufacturers.
It could be misfiring on two of the cylinders... Try a compression test first. If compression is low between two adjacent cylinders it might be a head gasket. If compression is up across all cylinders, it might be a coil-pack. The cylinders that AREN'T running should be obvious, since you should see that the sparkplugs are darker, fouled and/or soaked.
If you're only getting a lean indicator and no other problems you might have a vacuum leak or possibly a problem with the EGR valve. The multiple misfires (assuming P0300 or specific cylinders, P0301 ~ P0306) sound like lack of fuel to the injectors causing misfires, also resulting in O2 sensors "sensing" lean mixtures as a result.