CEL and no acceleration

NissanZ34

I do not have the cable or the dongle. I called the dealership mechanic and he said the flashing was a misfire and it could be due to an air leak or bad connections more than likely. He asked about the P300 code and I told him I did not get that code meaning it should not be real knocking otherwise I would have had that code or if it stopped knocking the code may have gone away by itself. The dealership mechanic suggested verifying all connectors are indeed well plugged in. He said unplugging the battery will not remove limp mode if there is but it will erase codes but still worth a try.