Ford Focus Forum, Ford Focus ST Forum - View Single Post - Question about post-cat O2 sensor
View Single Post
Old 07-22-2012, 09:43 PM   #14
Focus Fanatic
Join Date: Mar 2012
Fan#: 96610
Location: Fort Worth, TX
What I Drive: 00 wagon, 02 sedan both zetec atx

Posts: 4,808
FF Reputation: 23 amc49 Great Standing Member
Buy-Sell-Trade Rating: (0)
A plugged cat will run worse at higher rpm if it is bad enough to affect idle.

Common to check for vacuum leaks by plugging all fittings you can temporarily and then testing idle quality. Once the plugins are isolated as good then you go to gaskets and/or possible cracking somewhere to leak unmetered air.

See if the front O2 sensor is stuck low below .5 volt at warmed up idle. Indicative of a vacuum leak.
amc49 is offline  
    Reply With Quote