With the a/c on it idles properly. But it almost stalls when a/c is off, the rpms jump around until I accelerate then there is no problem until I return to idle

Did it suddenly start doing this? Or did you do some work on the engine? If it just started by itself whatever controls your idle speed is not working. You may have an idle air control valve or idle air control motor. The best thing is to go to a dealer and spend the roughly $50.00 to get a service manual. My '86 626 had an idle air control valve. The book showed where it was and how to test it. The Haynes computer control codes book also has a lot of generic tests to perform on sensors and output devices. These two books and a multi-meter and test light will solve most of your problems. As a simple test find the idle air control and with the engine running unplug it. No change, part bad. Engine dies, part good.