1983 Lincoln Mark Vi Went Advance Autozone Told Them Needed Idle Air Control

ok went to advance and autozone and told them i needed a idle air control valve.and they said they didnt know what that was also it runs ruff at idle and it idles up and down put it in gear and it dies and if it don t die it has no power no smoke at all motor sounds good when you give it gas in park but idles up and down ,put it in gear dies, and if you give it gas it will stay running in gear sometimes but no power and i don t know what or where the idle air control valve is or what it looks like