Are you the original owner? If not, then the injectors may have been R&R'd at some point in the lifecycle. If you have another vehicle, pull the injectors and send them to Witchhunter for cleaning/flow-balance-testing. If they test bad, then, you'll know which if any to replace.
They can be a biatch to pull, but I've found WD40 or Kroil with some initial twisting to loosen everything helps, plus a good slip-wire through the hole and pull while twisting gets it done.
- Pro dilectione Dei et patriam -