Too lean or too rich?
 

I've noticed that while holding a very steady throttle at certain speeds the check engine light will come on...
if i back out of the throttle for a few seconds then resume my previous speed the check engine light goes off...
do you think it's a too lean message from the 02 sensor or too rich that makes this happen?

Are you storing a code after the CEL comes on?
I am going to guess lean...I think rich might be accompanied by black smoke.
I have a hand held A/F meter that I run on my Camaro which would show in real time but other than the code, or maybe a odd spark plug if rich, I can't think of another way to tell...

Any misfires?

Definitely check the code. It may or may not store a code, so a real time check while running would be essential here, but checking for a code is where I would start. That and a can of Seafoam.

Seafoam:
https://amzn.to/2H5Liob

Runs perfect... just the light comes on... back off it goes away. ... our other 87did this same thing...
it did it on a more regular basis... this turbo 4 runner has only done it a couple of times...

I don't remember how to check code...

From memory, KNK, vss, and EGR temp are running codes.

Hmm ... That's pretty basic.
http://web.archive.org/web/201211190...85diagnosi.pdf
15 of the codes are stored in memory, including 25 and 26.

Ah, correct. I don't know much about the older models. Perhaps this will help:
http://www.4crawler.com/4x4/CheapTricks/TroubleCodes/

nice ... thanks for the link... good info
another project in the shop 25 degrees outside, I'll try pulling any codes when it warms up a bit or the shop gets space whichever comes first
it's not a pressing issue...
thank you for the input gentlemen

I used to have a Corolla that intermittently lit the CEL as you've described. I could predict when it was going to happen, highway cruise conditions. It was related to the catalytic converter catalyst being consumed. All else was fine and it ran with no problems. Is your cat original or less than a few years old? The cheap replacement I put on lasted 3 years. The original lasted more than 12.

No cat