Need Help with 4-runner

I have a 93 Toyota 4 runner and it wont stay idle once it is warmed up. If I have the air conditioner on it will idle and I have to go get it smogged. The code that we got was 24 & 31 but I dont know which one to replace. I am afraid to replace one and then it really be the other code that is causing the issue. These are rather pricey parts. Can anyone give me some advice????? Thank you! Georgene