We recommend you make sure your Infinity I30 is getting vacuum to the EGR valve. Manually open the valve, if possible, while the engine is at idle and check for engine idle drop. Your Infinity should stall or come very close to. This will indicate the EGR passages are open. If no RPM drop, the passages are still plugged and need more cleaning. If there is idle drop then look into why the EGR valve might not be receiving manifold vacuum required to open the valve during part-throttle and light load.
Other reasons for high NO include: Bad engine cooling, lean fuel condition and/or high mileage (carbon buildup).
Bad Engine Cooling - If your Infinity I30 has cooling system problems chances are excessive NO is being created. NOx (Nitrous Oxides) is created when an engine's combustion chamber temperatures reach over 2500F. A bad cooling system will create NOx.
High Cylinder Compression - Carbon build-up within your Infinity's engine combustion chambers will cause increased engine temperature and high NOx. Carbon build-up causes increased cylinder compression, which causes high temperatures, which result in high NOx emissions.
Lean Fuel Mixtures - Lean fuel mixtures cause high NOx also. A lean fuel mixture is when the engine receives less fuel then is necessary to obtain efficient combustion. Lean fuel mixtures are often due to vacuum leaks and/or defective emission sensors which report air/fuel mixture amounts to the ECU. A good example of such component(s) is your Infinity I30's oxygen sensors.
