DTC Description

The temperature of catalyst has an effect on emissions. Also, the PCM estimates the temperature of catalyst by intake air mass. By the way, the intake air mass is in proportion to RPM controlled by ISCA during idling. So, if the Integral of deviation between set point RPM and actual speed RPM is out of the threshold value, the PCM judges that ISCA doesn't work properly. And it could be a reason of bad emissions.