I have a 96 Z28 that a new LT1 engine has been put in , it is getting a code that reads p1641 undefined code. Does anyone know what that is? I have a chiltons book on it and that code is not in there. here is what it is doing or not doing. at a cold start it runs perfect but after about 5 min it starts to run rough at a idle but smooths out after a hesatation when hiting the accel. it almost sounds like a misfire but im not getting a code for a misfire.... can anyone help... thanks

fan control relay 1 control circuit. heres a link for codes defination
http://www.troublecodes.net/GM/

thanks that took care of the p1641 code , but now I have a crankshaft position sensor malfunction and a crankshaft position sensor out of range performance code, i already replaced the sensor with no help..

lol i just posted in the new thread you did to fix that problem