Poor idle when radiator fan comes on?
 

I have an 08 automatic Corvette. What would cause idle misfire when the radiator fan comes on about 50% or more?

The fan presumably adds load but maybe the fan coming on,
is only indicative of an even higher load (A/C) or elevated
engine temps. The engine may still be within the same trim
cell but now it's at a MAP-point that is different and may not
like the trimmed mixture, or may not even like to idle as clean
at stoich.

Might try looking at how much higher MAP goes and whether
the fan itself is to blame, or if it's just a telltale for something
else. Expect there are airflow adders for fan, but you might
look for anything that lets you bump spark (more, or less?)
based on fan and other accessory loads as may be appropriate.
I've never looked at anything newer than LS1/LQ9/LS6 myself
so this is all I can suggest.

I have a log I ran with HP Tuner that shows the 02s dropping after the fan comes on. I could email it to you. Apparently it goes way lean as best I can tell. AC on high fan does not have any effect on idle. Only the radiator fan. I've tried more and less timing but does not produce any change in idle with the fan on. Might note too that in CL idle is not good even with fan off. In OL idle is good, not like it should be, but when the fan comes on once again unacceptable idle. Did not log MAP but could run another log to get it.