what code reader do i use

i have a 1995 chevy blazer LT 2wd the check engine light keeps comming on but will go off when i turn the car off and turn back on but when it comes on the idle flucuates, well i have a gm code reader from 1982-1995 but it doesnt plug into my blazer all the other code readers are 1996 and newer, what kind of code reader do i need to buy and does anyone have any ideas of what it could be. here is a piture of the code reader i have. thanks for the help [img:84b3e4e410]http://www.2carpros.com/forum/automotive_pictures/54950_3123_1.jpg[/img:84b3e4e410]