Originally posted by DemonSVT:
Originally posted by todras:
How do think the car gets air to idle? 
The idle air control valve. 
Next obvious question please? 
The hole in the throttle plate is there to help equalized the air pressure on both sides of the plate. This means you do not get as turbulent a spike when the plate opens.
The size of the hole was used as a tuning aid by knowledge tuners in the days before electronic engine controls. I suspect that it could be used in the same way today. Especially with a cam change where the idle speed needs to be raised, you can accomplish the same thing as cracking the throttle plate open a little more by gently enlarging the hole. This will help keep from upsetting the throttle position sensor reading. In the case of carburators, enlarging the carb throttle plate hole kept the proper relationship with the vacuum ports and various linkages (choke, accel pump).
Jim Johnson
98 SVT
03 Escape Limited
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