For what it's worth.....from the Service Manual:This is also true..Alot of people dont realize by adding CAI, Exhaust,Headers,test pipes,ect..Your increasing the ability of the engine to breath,which makes the A/F ratio run leaner, as in your case,dangerously lean..Although N/A cars are a bit more forgiving,they will detonate themselves to death with an A/F ratio of 15.3 on 91 octane and aggressive timing such as the timing the Z already runs..At your point a reflash or a method of tuning and adding fuel is a must for safety as well as untapped power and getting the most bang for your buck on your N/A mods. The ECM will not compensate for that lean of an A/F ratio in open loop no matter what you do.It has a set parameter it works off of based on MAF readings that at some point becomes limited in its ability to compensate fuel and timing, at which point knock is inevitable.When knock is detected the ECM will switch into a low octane mapping , robbing you of any power you would have made with your mods.Most people confuse this map switching for the ECM LEARNING MYTH..
DTC P0171, P0174 FUEL INJECTION SYSTEM FUNCTION PFP:16600
On Board Diagnosis Logic ABS000W4
With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the
theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. The
ECM calculates the necessary compensation to correct the offset between the actual and the theoretical
In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the
ECM judges the condition as the fuel injection system malfunction and light up the MIL (2 trip detection logic).