help with check engine light

[gearhead37683]

hey guys i have a 95 gst with a 6 bolt engine, and everytime i drive it after around 30 miles the CEL comes on and the car starts running rough, i can unhook the battery and it resets the light and i can go another 30-40 miles then the same thing happens CEL and runs rough. i tried the key on key off test to retrieve any codes it might have, but the check engine light just stays on it doesnt blink for any codes or anything. does anyone know where i should start on this thing. im afraid if i take it to the shop to have the codes read it might not come up with anything. and i will be out cash, so please any help will be aprecciated. thanks alot guys

 

[Bannery]

Key in the ON position but engine not running?

But the engine runs,
Is this device not compatible possibly to it?
autel maxiscan ms300 + Mitsubishi eclipse 1999 (420a)