First look through the L-jet Spider Diagnosis page (link below) for lots of things you can do at home. L-jet is a system - all the bits have to work right for it to work right.
Keep in mind that L-jet is very intolerant of air/vacuum leaks so look very closely for any problems there - loose clamps, split hoses, etc. Also the OVS (Oil Vapor Separator) can get clogged and mess with sump scavanging which makes it act like an air leak. Soak the OVS in solvent, rinse & repeat until you get out as much gunk as possible.
How old are the spark plugs, wires, cap & rotor? And the fuel filter?
If everything cheap & easy checks out then consider having the fuel injectors serviced. See the link below to OK injectors for more info about what they do.