Tachometer stopped working after engine replacement
 

I just replaced the engine in my 02' Santa Fe with a 2.4 and when I first got it running it was running rough because of old gas & fairly old plugs & wires. Now after having the engine running for a while just to make sure everything was ok, the tachometer was "twitching" between 0-1000 rpm but the idle never changed. I went over my work & everything was fine nothing disconnected or broken... any ideas what it might be?