problem. Never put injector cleaner in your Z the Z hates it for some reason and just that stuff is crap anyways and doesnt really do a good job. You need to fix your Det code because it could be possible you had detonation from the fuel cleaner being added some how. You can try and reset the ECU by pulling the battery cables for an hour or so or its very possible your Det Sensor is bad and may need to be replaced.
In my opinion I would try to do a compression test to make sure you didnt destroy the motor by any chance because emissions can be affected by bad compression.
Also fill out your profile unless your car is stock but in any case list miles or something it helps all of us help you out.