definitely makes an OBD2 car run richer...because adding 100-200 cfm intake air volume to the engine, it far beyond what the ecm was programmed to handle, with idle setting throttle body opening. where the lambda duty cycle on my Mercedes V12 M120 was 50-60 before, it jumped to the 60-75 range. Much richer. so much so, it would burn your eyes out sitting there idling. and the link shows it's happening often.
the factory ecm must be REPROGRAMMED to input the new airflow being passed by the KN filters, as normal.
otherwise, it sees it as a vacuum leak of sorts