Quote Originally Posted by steveo View Post
no other engine modifications?
There were - solid lifters and larger IAC bypass holes. But this problem started as soon as it started to get hot & humid, well before any modifications. Nothing really changed with the addition of the lifters.

Cracking the throttle a bit made a huge difference. The MAF was actually registering slightly less airflow at the same engine speed. I'm working on checking hot valve lash so can't post too many details. Will try a cold start in the morning and post an update.