Please help! Idling issues.

[1990 NC SSP]

I completed a base idle reset again and it seemed to be idling ok. When I turn the heat the idle lowers and nearly turns off. I will see how she runs in the a.m.. My car has motorcraft spark plugs, but it need to probably change them soon for a tune up. There is also a pretty bad exhaust leak on the passenger side I will address as soon as possible. I wish she was ready for the 50th Anniversary Mustang car show in Charlotte, but she is not ready. Maybe I will be able to show my car at the 51st Anniversary next year. Thanks for all of the help.