Running lean..... in warm weather?

[mightymax37110]

My father recently passed down his 93 mighty max to me since I'm recently out of prison and starting over. Well it needed a mass airflow sensor, after replacing it ran great. In the winter weather. Now that it's warmed up some outside in the great state of TN, in warm weather, and after it has reached normal operating temperature it runs lean. This is by the way a 93 mighty max 2.4

Anybody have any idea of what is causing this? I'm stumped. Between my dad and myself we have 60+ years of mechanic experience and neither one of us can figure it out. I found your site and joined in hopes someone, anyone can help me out.