Won't resond above rough idle, throttle to the floor

1994 Cavalier 2.2L 4 cyl. Manual trans. When I start it, I have to have gas pedal floored & keep it there or it won't stay running. Runs at a rough low idle. Some days I can get it to run (gas pedal released) idle a bit rough, but it will respond to pressure on pedal. I drove it down to the mailbox & back ( about 2 blocks) & it goes back to above mentioned response. Any ideas? Thank you for any help.