well when first tuning and you have done major changes that the car wont idle or you just want to correct the idle...the first thing to tune is idle...once you have corrected the idle...you can move on to part throttle and then WOT tuning...once that is figured out...you fine tune to a certain AFR

and yes humidity, altitude, and temperature can affect the cars performance in different settings and why alot of cars that are tuned in the winter as said above will blow up in the summer...which is why alot of tuners recommend a safe tune for both or if available will have a switchable tune for summer and winter...depending on the tuner and software being used

 

This what I have seen, Most RWD cars tend to be seasonal so they can run on one setting/tune for that season but be it with HHR's and the likely hood it would be a year round useage, drivers need to be aware of that.

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Thanks!

 

Thanks for the feed back !