CEL on then off again

[KoopaTroopa]

Swapped a cali spec 5 speed into my fed spec automatic 240. Engine light is acting strange, sometimes it comes on when driving but then turns back off while i'm not moving in traffic. Sometimes it seems to come on when over 2500 rpm but other times it won't. I figured it needed a restart so i left the battery disconnected overnight but it didnt change anything. I've always thought that once you threw a code the cel would stay on until that code had been erased? not on and off while the rpm's change.

CEL is for egr temp sensor btw