Very rough idle, PO161 code - F150online Forums


Very rough idle, PO161 code

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  #1  
Old 08-12-2008, 01:55 PM
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Very rough idle, PO161 code

Well it's been a while since I've broken my truck, so it's good to see you all again.

About two weeks ago my truck started idling really rough. The RPMs drop to 500 then surge up to around 1100, then start over again. My truck has 130k on it and the oxygen sensors have never been replaced so I thought that was most likely the problem. Replaced the two primary sensors and the truck still idles horribly. I've been told all sorts of things: PCV, TPS, O2 sensors, bad cats, IAC, etc...

So I scanned the codes and came up with a PO161, which is some sort of malfunction in the downstream driver O2 sensor. While doing some inspecting around there, I noticed that the wires on the downstream passenger O2 sensor have worn through and are possibly grounding on the tranny mount. That one obviously needs to be relaced.

So I want to know if I can expect the truck to run fine after replacing the back O2 sensors. If not, what should be the next step I take?
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Old 08-12-2008, 02:01 PM
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Quote:
Originally Posted by jiggle View Post
Well it's been a while since I've broken my truck, so it's good to see you all again.

About two weeks ago my truck started idling really rough. The RPMs drop to 500 then surge up to around 1100, then start over again. My truck has 130k on it and the oxygen sensors have never been replaced so I thought that was most likely the problem. Replaced the two primary sensors and the truck still idles horribly. I've been told all sorts of things: PCV, TPS, O2 sensors, bad cats, IAC, etc...

So I scanned the codes and came up with a PO161, which is some sort of malfunction in the downstream driver O2 sensor. While doing some inspecting around there, I noticed that the wires on the downstream passenger O2 sensor have worn through and are possibly grounding on the tranny mount. That one obviously needs to be relaced.

So I want to know if I can expect the truck to run fine after replacing the back O2 sensors. If not, what should be the next step I take?
what year is the truck, if its new enough you might check the mass air flow
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Old 08-12-2008, 02:19 PM
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Disconnect the battery, fix the broken wire. Re connect the battery (it should have been disconnected for at least 15 minutes I'd think).

Start the truck, but DON'T touch the gas pedal or do anything, other then let it idle for a few minutes... It'll rise up and down some initially, but it's just adjusting itself and then it 'should' find it's idle and run fine....

Take it out and drive it around and then see if the code pops up again. The initial code could be just because of the broken wires??

Anyway, it's the computer and other sensors and hardware that control the idle, so start there first, then start trouble shooting...

At least, that's what I would do...

Mitch
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Old 08-12-2008, 05:21 PM
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I forgot to mention the auto parts store was nice enough to let me put in a new TPS in their parking lot to see if it would help. It didn't, so that's another thing ruled out. Assuming the weather holds up, I'm gonna go clean the MAF and try to repair the grounded wires in a bit.

Thanks for the help thus far and keep the replies coming.
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Old 08-12-2008, 07:07 PM
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Turns out the wires were not exposed so that's not causing any problems. I took the whole intake off and cleaned it all, along with the MAF sensor. Also cleaned the throttle body, as it was looking pretty nasty. The truck still runs like crap.
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Old 08-12-2008, 07:13 PM
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Same thing happened to me When I installed my intake best advice is just make sure everything is SUPER tight. Just my 2 cents
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