my check engine light's been turning on on me on hot days. i drive it at night and runs ok and the CEL doesn't turn on. when i drive it during the day when it's hot the CEL turns on. today it's 113 outside and i was driving for a bit. not even too far. turned it off and when i tried to turn it on again it struggled. it's a '93 xj with 'bout 93G miles. manual trans. anybody?