After the exhaust upgrade, I think MPG actually improved about 3/4 to 1 mpg. However, I think the CAI took all that away and more. I am not sure if my engine has ever recovered from the CAI. Does anyone know (Nitro Tech) if the small electronic sensor in the intake near the throttle body is the mass airflow sensor? If I got oil on it what would happen, and is there any way to clean it or do I just need to replace it. It does bug me that my mileage went down when others say they have seen an increase.
A side note for mileage. When I first got my Nitro, it was getting about 19 mpg around town. A week later, I took a 375 mile round trip on the interstate. That pushed the MPG up to about 23 mpg. Afterward and since that time all my mileage has been around town driving, now approx. 1,600 miles total. It was in that second week of ownership that I had the exhaust installed. For the remainder of the week afterward, I still saw city mpg around 19. The next weekend was when I got the bright idea to install the CAI. For that next week, I checked mileage daily, with each day getting slightly worse, down to a low just under 15 mpg. The next weekend, I put the stock air-box back on and the mileage rebounded to about 18 mpg. I can't get it back to 19 mpg and I am very conscious of my driving habits.
The engine runs absolutely great. One thing I did notice immediately upon reinstalling the stock air-box. The engine surge at cold start up was back. I had not noticed that it was gone completely with the CAI installed. I miss this with the CAI. With the stock air-box I have to let the engine idle down before dropping it into reverse, otherwise I get an rpm surge and the vehicle will lurch backward. This is not defect. I realize what is happening when the engine is cold, the computer is requesting a specific fuel/air mix. With the stock air-box, the rpm has to increase to about 1300 rpm to satisfy these requirements. With the CAI installed, the engine did not have to rev up past 1000 rpm to satisfy the oxygen side of the fuel/air mix so this eliminated the surge on cold start and the subsequent lurch if dropped into gear too soon.