4.6 rough idle
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Joined: Apr 2013
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4.6 rough idle
Hello all, new member
I just bought a 2008 STX 4x4 with a 4.6, 109000 miles. It has a rough idle thing going on.
What I've done:
Cleaned throttle body
Cleaned MAF
Cleaned PCV valve
Replaced plugs with Motorcraft OE plugs
It's throwing a P0420 - one of the cats is new, one is not. The one that's not is being replaced tomorrow. It also has a pending code of P0316 - misfire at startup in first 1000 RPM's. It doesn't have a code specifying which cylinder.
Can a bad cat make it misfire? What else can I do to try to get it to idle smoothly? Acceleration seems normal (as good as it can be with a 4.6) but the rough idle annoys me.
Any suggestions would be welcome.
I just bought a 2008 STX 4x4 with a 4.6, 109000 miles. It has a rough idle thing going on.
What I've done:
Cleaned throttle body
Cleaned MAF
Cleaned PCV valve
Replaced plugs with Motorcraft OE plugs
It's throwing a P0420 - one of the cats is new, one is not. The one that's not is being replaced tomorrow. It also has a pending code of P0316 - misfire at startup in first 1000 RPM's. It doesn't have a code specifying which cylinder.
Can a bad cat make it misfire? What else can I do to try to get it to idle smoothly? Acceleration seems normal (as good as it can be with a 4.6) but the rough idle annoys me.
Any suggestions would be welcome.
Last edited by ophidia; Apr 17, 2013 at 11:28 PM.
Senior Member
Joined: Dec 2006
Posts: 43,530
Likes: 817
From: Joplin MO
A plugged cat can make it run like total crap.
Did you use dielectric grease in the cop boots when you changed the plugs? Might want to throw a bottle of Techron in the gas in case the injectors are getting dirty.
Did you use dielectric grease in the cop boots when you changed the plugs? Might want to throw a bottle of Techron in the gas in case the injectors are getting dirty.
