Have an 84 t-type that I bought two months ago. Previous owner didn't take care of it so trying to get it right. Car idles fine when i shift into gear it feels like it's going to stall but doesn't. I can take off and drive it but when I slow down/stop the car stalls out. I can turn it right back on and drive it again with no problem until I have to slow down or stop. What is causing it to stall? (Newbie btw)