I’ve slowly been trying to get my 87 GT, which is almost 100% stock(full exhaust and a TB), to idle like it doesn’t have a letter cam. The other day I replaced all the vacuum lines, and dumped the computer codes, and now have just a code 85, which is canister purge valve. Will this thing cause a rough idle if it’s bad? Is there a way to test it? I don’t really want to spend $60 on a new one if it doesn’t do anything other than get rid of the fuel smell.