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Old 07-22-2012, 10:29 PM   #15
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Join Date: May 2012
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Location: Springfield, OR
What I Drive: 2003 Focus SE

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Originally Posted by amc49 View Post
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.
That's a good tip. I'm pretty sure the front O2 sensor is getting above .5V .. in all cases it seems to be between .1V - .9V, but I will double-check.

Originally Posted by BC_ZX3 View Post

While the vacuum tubing is some kind of special hard plastic - crimps fairly easily btw - the connectors clustered at the top of the manifold are simple push on rubber fittings (except for the big EVAP fitting). You can pull them off one at a time and inspect. Try blocking the port temporarily and see if the idle improves to try isolate any offending line.

Did you replace the PCV elbow and valve (front of the engine) when you repaired the collapsed rear hose?
I did replace the valve itself, but not the front elbow. It seemed in OK shape - no obvious splits or collapses.

I did another spray test this afternoon and noticed no change in idle. I also fiddled with all the connections, and again, nothing.

Besides codes, should I notice any change in performance when removing and plugging vacuum lines? I want to make sure I'm diagnosing the original problem and not noticing artifacts of the missing vacuum...

Thanks again for all the help.
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