My light came on briefly when driving it, and it's been running rough in the morning. Mileage 16-19 without air conditioning.

i bought a scanner-actron cp9001, plugged it in and ses light stays on when i turn the key to on, NOT starting the motor.
It's a 1994 v6 camaro ODB1 sticker, so Im pretty sure Im doing everything right.
the scanner book says try the manual cuz it must blink a code 12 no matter what. the haynes manual has NOTHING regarding a non-blinking light when scanner is plugged in.
Any ideas? thanks