OK. You can upgrade the injectors but that still doesn't mean that there isn't something else going on. How about a small tear in your intake boot? The clamp might not be tightened down all the way? Just those would cause your car to rough idle and lose mileage.
There is more to it. Could be a tired motor too.
You might want to find a good mechanic that knows these cars and have him go through the car completely and see what he finds. Always better to have more eyes on an issue instead of just throwing time, parts and money at it in my opinion.
HTH
Cheers,
~Ralph