I've been working on a tune for a few months now, and things are looking up. I made a run last night, the off idle stumble was gone, as well as the low rpm shudder when the TCC is locked. On the way home, I turned the a/c on, and the stumble/shudder returned. I have seen that the IAC counts will be low with the a/c off (30 or so?), and higher,(90 or so?) when it is on. What is the correlation, and how do I correct the condition?

 

The IAC is opening due to the additional load of the A/C compressor along with a bump in the idle speed. The cam being used adds to this as the more duration the more overlap and the less low speed power.

Additional spark advance can help in this regard. Can also bump up the idle speed.

RBob.

 

Thanks, I'll give that a try.