The stock narrow band 02 sensors are looking for 14.7 to 1 air/fuel ratio. The ratio of 14.7 to 1 worked perfect for stock cars with the fuel we had when these cars were new. With today's fuel that has ethanol they like to run a little richer to have a perfect idle. Also when you remove back pressure by going to larger pipes and deleting cats, the engine also likes to be richer than 14.7 to 1. Small air leaks in the exhaust before or near the 02 sensors can cause the sensors to push for a even leaner Idle/cruise mixture. With today's fuel and a modified car that does not have cats, a perfect smooth idle requires a AFR of about 13.5 to 1. What you can do to check to see if the 02 feedback is causing the rough idle, is simply unplug the 02 sensors before starting the car and see how it runs. You do have additional fuel in your program for today's fuel since your running our program. But the 02 feedback is standard to keep from having problems passing smog. We can work with you and make changes to your program to get a smooth idle. We will need you to get AFR numbers for us to make sure you do not have other issues.
