Now that I'm running the AC due to hot weather, I have noticed that the idle control motor range appears to be insufficient on the PTM 102mm throttle body to reach 950 engine RPM
with AC on and the car in gear. This is most likely because I now have longer duration camshaft (238 by 242 degree) that results in less intake manifold vacuum at idle, and I now
have a situation where it appears I'm exceeding the idle air control motor range. (I'm still using the stock 2000 GM version of the PCM program).
When the engine is warmed up, it idles fine at 950 RPM with the (1) transmission in park, (2) AC compressor off, and (3) idle control motor IAC counts at zero (minimum possible) and
with the throttle blade screw at maximum opening.
The throttle blade screw must be at maximum opening otherwise there is insufficient idle air for cold winter starts; the throttle blade screw must be at its maximum position with IAC
counts at the 310 maximum possible. Anything less than maximum throttle blade screw position simply will not provide the total amount of air needed for a cold winter start.
NOW with the AC compressor on and the transmission is in gear, the idle control motor runs out of IAC counts (310) at about 850 RPM, so it is not possible to reach the desire idle of 950 RPM
with AC on and car in gear.
Is there anything I can do other than switching to electronic throttle control throttle body? I strongly prefer not going to the trouble OR expense of converting my car from throttle cable to ETC.
Thank you very much for your help!
P.S. TPS and IAC motor are both new, both have valid voltage ranges and are working correctly. I just barely had enough range during winter, and with AC I have now exceeded range.