QUOTE(unitron @ Jul 20 2013, 05:42 PM)
O2 sensor faulty normally got check engine light.... plus bad fuel economy. Have to scan for fault code and monitor closed loop feedback with OBD2 scan tool to check.
Never worked on a Vios engine.. but normally throttle valve is fully closed during idling for cable driven TB. Air metering in to keep engine running in idle is control by a separate IACV.
Very weird that Vios doesn't use similar setup with IACV but got screw to adjust throttle valve directly for cable driven.
My guess is O2 sensor faulty will only throw up CEL if it is not responding. If it is feeding bad data to the ECU, the ECU won't know anything is wrong. My friend didn't encounter CEL also until he completely stalled.
the idling screw serves as some sort of easy override on top of the IACV control. This is not limited to just the old Vios, most cable driven TBs have this.
EDIT: my mistake, it doesn't adjust the throttle valve directly, but rather the opening of an alternate air flow route.This post has been edited by dares: Jul 20 2013, 05:56 PM