I think it's somewhat the nature of the beast. The "cold start" emission certification starts at room temperature and it's always been my experience that cold starts at 40F are better than 70F. Since most emissions are produced during cold start and warmup, the cold start calibration at shirt sleeve temperatures is on the ragged edge of leaness.

After cooling for 20 minutes the engine temperature is in this netherworld between not hot, but not really cold.

It's my opinion that better cold start performance in mild weather can be obtained by setting the duty cycle to less than 50 percent at idle, but I would not go below 40 percent. The lower the duty cycle the richer the basic mixture, which is what is applied before the KE system goes into closed loop operation.

In case you aren't familiar with the duty cycle and its adjustment the following site has a very good writeup.

www.landiss.com/mixture.htm

Duke