The computer should go closed loop at idle and look at the HEGO sensors to set mixture. The "adjustment" has limited range however. Larger injectors can result in the EEC not being able to bring the fuel within range.
A second thing that can cause this is excessive idle fuel pressure. The fuel regulator should have a vacuum line to the engine manifold vacuum. This line reduces fuel pressure when engine vacuum is high. Some aftermarket regulators do not monitor engine vacuum.
Assuming your HEGO (oxygen) sensors are good and the computer is going closed loop and has normal idle voltage (below 1.2 volts) from the throttle position sensor, it is probably injector size or fuel pressure.
By the way, I had good mixture using 19 lb injectors with 300-350 RWHP. I only have 39 lb injectors now with a supercharger making over 450 RWHP. Bigger injectors do not always mean more power.
Tom
A second thing that can cause this is excessive idle fuel pressure. The fuel regulator should have a vacuum line to the engine manifold vacuum. This line reduces fuel pressure when engine vacuum is high. Some aftermarket regulators do not monitor engine vacuum.
Assuming your HEGO (oxygen) sensors are good and the computer is going closed loop and has normal idle voltage (below 1.2 volts) from the throttle position sensor, it is probably injector size or fuel pressure.
By the way, I had good mixture using 19 lb injectors with 300-350 RWHP. I only have 39 lb injectors now with a supercharger making over 450 RWHP. Bigger injectors do not always mean more power.
Tom