1997 Cutlass P0306 Code

My girlfriend has a 97 cutlass with the 3.1. My scanner came up with a P0306 code. I replaced the coil pack and that did nothing. I've sprayed carb cleaner around the intake, tb and can't find any vacuum leaks (so far). I've check the plug, looks good and getting good spark. Engine mises at idle and you can feel it when accelerating. Replaced the MAP a year ago when I put head gaskets on it. It's been running like this for the past 6 months or so. Had a bad wire on the ignition module that was fixed last summer. Haven't checked injectors yet. Any ideas? Thanks

Tap #6 injector with a blunt tool.