Timing set at 10 degrees
Fuel pressure set at 38psi
Idle at 950-1000
New IAC and O2 sensors
Car ran great idled perfectly prior to the new air box. Surged after. How come? A/F showed pig rich. Tuned to pull A/F back down. Problem solved. What logical and reasonable alternative was there?
The elephant in the room is turbulence over the mass air sensor.
Other possible solutions:
Change the shape of the intake tract
Screen the sensor
re-clock the sensor
change the sensor
change the housing
Scale the sensor and housing assembly
change the distance between the MAF and TB
There are a number of things that can induce and support a surging idle in a closed system.