If you've disconnected the battery for at least 5 minutes or grounded the leads and it comes back then you've got a problem someplace.
13 - No difference recognized between the engine MAP reading and the barometric (atmosphere) pressure reading from start-up.
OBD-1 Codes are all the same. Actually OBD-2 codes are the same until they went to P Codes which are of course different.
So, you've either got a vacuum line leak or your MAP is dead like oldjeep said.