Hey guy, The problem is most likely caused by your car leaning out
What CPE & injen does to fix this is they have some form of chip with a new Fuel map to compensate for the boost in air flow as the stock ecu wont compensate for this much additional flow
Leaning out simply means your o2 Sensor is sensing more oxygen coming from the exhaust than is within acceptable levels, Basically you added too much air for the amount of fuel being given within those RPM ranges.
Running Rich means your o2 sensor senses NO oxygen which in turn means your car either is not getting enough flow through the intake or your injectors are pumping too much fuel into the mixture. (The more fuel you pump in, the less oxygen will be left over)
Now although what others may have said could be true, if this is not an Injen or CPE intake setup with the MAFC-I chip then your system verywell likely is leaning out... I know because i am experiencing the same issue however i'm slightly somewhat more pre-pared
My solution is going to be using a Piggyback Fuel control system IE: Apexi SAFC / SAFC II To compensate for the additional air, which is why i ALSO did not buy the CPE or INJEN setups because i have future plans with bigger mods & my Apexi unit will definately help tunning for those items (notice my threads posting for buying SAFC lol
Now if this is NOT the case with your car (the symptoms are identical to what i experienced) Please make sure your injectors are clean, your Throttle Body is not all tarred up & you have a clean fuel line & fuel filter
Let us know!!!
Also, for anyone that feels i miss-informed him PLEASE correct me
BTW, running lean CAN be very bad for the motor