Chanceg10

Lately my 86 vette has been losing a lot of power while driving but only temporally it is like there is a little hesitation when i get on the gas pedal and while idling it has dropped as low as 400 rpm or even died which is unusual. When i put the code reader on it was giving me 43 and 12 so i replaced the knock sensor and the pig tail wire and got rid of that code and now i'm left with just 12 which to my understanding will always be there. has anyone had this problem? Could it be the fuel pump?