Check engine light comes on/off only when engine is running & under load.

What is your question?

1991 jeep wrangler yj 6 cyl. 5 spd. Check engine light comes on/off with key turned to acc. Cannot use OBD1 scan tool because CE light does not stay on when engine is off and not running. CE light Only comes on while driving. Also, their is a stumble/hesitation in throttle response, from MID-WOT, from 2nd - 5th gear. Replaced gaskets, cleaned throttle body, replaced fuel filter & fuel pressure regulator. Fixed exhaust leak, fixed vacuum leak. Any and all ideas would be greagly appreciated as i am stuck at the moment on what is causing this issue!

What makes this problem better or worse?

Hard starting when e.gine is cold. Has low idle, at idle w/ no load.

How long has your 1991 Jeep Wrangler had this problem?

A couple of months