93 Hyundai scoupe with rpm problems

My check engine light is on and it deals with my rpm's . My rpm's are not working on my dash and it's causing a check engine light to come on concerning it... what would cause my rpm's not to work?? This is a 93 scoupe automatic with 110,000 miles.. just replaced the engine and engine runs well and shifts okay.. 2nd is a little slow and changing but for the most part it's okay..but I can't get this rpm problem fixed so that I can get it to pass emissions.. .. what should I do?