I recieved a p0300 code on my 99 grand prix 3800 gt. I replaced the spark plugs and wires($150.00). I then replaced all of the coil packs ($80). Replaced the catalytic converter($250). I've tried stp fuel injector($7) and fuel cleaner. I've had two full diagnostics ran in order to find out EXACTLY what the problems were(both $100) one from tires plus and one from pep boys. All reports back to me were false, stating that it was either the coil packs or the module underneath the coils. Had the ICM tested 3 times and it works perfectly fine. I've even listened to all advice here, thus having exhausted all of my resources. I don't know what to do. I could try replacing other things (fuel injector, fuel filter, air filter) but that would only cover a few things that MIGHT be wrong with it, leaving even more expenses I'd have to deal with (vacuum leaks, low fuel pressure and GOD KNOWS WHAT ELSE.) I've been missing a lot of work due to coworkers not able to consistently give me rides and the closest bus being 45 min walking distance away from my work. On top of that I think my boss is getting sick of the same excuse. I don't know what to do.