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Discussion Starter #1
Truck started to idle very roughly when the RPM dips below 700. No CEL. It all started after an oil change (could be a coincidence), I changed oil, cleaned air filter, cleaned the TB, checked all spark plugs, cleaned MAF, even seaformed it. But it still idles hard right around 700 RPM.

I am baffled. Any input would be appreciated.
 

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Miles?

Replace front O2 sensor, MAP sensor.
The O2 sensor is cheap and needs replacement at 60K or so for good idle, fuel mileage, and best driveability.
The MAP sensor is very cheap and can be replaced in 1 minute with no tools.

You want it to really idle like new, in addition to the above replace the engine mounts.
 

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Discussion Starter #3 (Edited)
87k Miles on my 06 I5.

If it's the O2 sensor, should the CEL be on by now?

Could it be the knock sensor?
 

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..If it's the O2 sensor, should the CEL be on by now?

Negative... I learned this the hard way after dealing with rough idle for more than 2 years.
If the O2 sensor goes totally bad, then yes there would be a CEL.

At about 60K - 65K though the sensor just begins to drift a bit, returning a signal that's well within range to drive ok, but not quite accurate.
When that happens it effects the idle far more so than above-idle speeds.
At 87K that's more than enough miles that if it were me I would replace it.
You'll feel at least some small improvement on acceleration and all-around driveability also, and your fuel mileage will improve a tiny bit.

The MAP sensor affects idle greatly. And it's so cheap and easy to replace that it's worth doing at any rate.
(notice, that's the MAP sensor, not the MAF)

You should also check for vacuum leaks of course.

I'm nuts about my truck, and I actually like the I-5, but after 2-3 years of rough idle I was really loosing patience with it.
New plugs, O2 sensor, and MAP sensor did it for me. It now idles great, except for the very occasional tank of weak fuel.

Hate that I suffered with rough idle for so long when the solution was so easy.
I just thought it was because of age and miles. I was wrong.


3 weeks ago I replaced the engine mounts and idle is even better now. Much better. It feels new again at idle, or damn near.
My truck is an '05 with 136K on it though.
Knowing what I know now, I'd be looking to replace the engine mounts by 100K if I had it to do over again.
The mounts loosen-up with age and that allows the engine to rock back-and-forth more, which you feel very much at idle.


Could it be the knock sensor?
As far as I'm aware, not unless it were really bad.. I mean total failure, and then I suspect you'd get a CEL.

I don't think the feedback from the knock sensor is really evaulated by the PCM at idle..
I may be wrong about that, but to my understanding the knock sensor wouldn't be a factor until you're under load.
I do know that it isn't a common cause of rough idle..
 

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I was just thinking about this last night. Mine is an 05 that just hit 50k and is idling roughly. The only code I'm getting is an Evap vent control circuit, P0446. I'll probably plan on changing my sensors out in the next couple of weeks. Should I replace both the upstream and downstream O2 sensors at the same time?
 

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I was just thinking about this last night. Mine is an 05 that just hit 50k and is idling roughly. The only code I'm getting is an Evap vent control circuit, P0446. I'll probably plan on changing my sensors out in the next couple of weeks. Should I replace both the upstream and downstream O2 sensors at the same time?
Wouldn't hurt.

I didn't though. I plan to do so soon.
As I was told by folks here at 355 Nation, the rear O2 sensor is there to monitor the condition of the catalytic converter. It's the front sensor that counts for idle and driveability.
 

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Discussion Starter #7
Negative... I learned this the hard way after dealing with rough idle for more than 2 years.
If the O2 sensor goes totally bad, then yes there would be a CEL.

At about 60K - 65K though the sensor just begins to drift a bit, returning a signal that's well within range to drive ok, but not quite accurate.
When that happens it effects the idle far more so than above-idle speeds.
At 87K that's more than enough miles that if it were me I would replace it.
You'll feel at least some small improvement on acceleration and all-around driveability also, and your fuel mileage will improve a tiny bit.

The MAP sensor affects idle greatly. And it's so cheap and easy to replace that it's worth doing at any rate.
(notice, that's the MAP sensor, not the MAF)

You should also check for vacuum leaks of course.

I'm nuts about my truck, and I actually like the I-5, but after 2-3 years of rough idle I was really loosing patience with it.
New plugs, O2 sensor, and MAP sensor did it for me. It now idles great, except for the very occasional tank of weak fuel.

Hate that I suffered with rough idle for so long when the solution was so easy.
I just thought it was because of age and miles. I was wrong.


3 weeks ago I replaced the engine mounts and idle is even better now. Much better. It feels new again at idle, or damn near.
My truck is an '05 with 136K on it though.
Knowing what I know now, I'd be looking to replace the engine mounts by 100K if I had it to do over again.
The mounts loosen-up with age and that allows the engine to rock back-and-forth more, which you feel very much at idle.
Thank you kindly Sir. I will be soon putting an order in get two new O2 sensors. I just went out to check the upstream O2 sensor. Since I dont have a O2 socket, I didn't want to mess around. One thing I noticed though, the connector is mounted by using a spiral plastic screw (from a picture of the sensor I found online). To take the connector out, Do I just pull on it?

Here is the picture of the O2 sensor.
 

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Discussion Starter #8
Also, Where are the engine mounts located in your truck?
 

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Thank you kindly Sir. I will be soon putting an order in get two new O2 sensors. I just went out to check the upstream O2 sensor. Since I dont have a O2 socket, I didn't want to mess around. One thing I noticed though, the connector is mounted by using a spiral plastic screw (from a picture of the sensor I found online). To take the connector out, Do I just pull on it?

Here is the picture of the O2 sensor.
Don't really know about that..
I didn't do the work myself. I'm a long way from home and had a shop do it for me.
(I did swap the MAP sensor.. no tools and no lift required :D)

It does look from that picture that you'd just tug that retainer up.

I have a little tool from Lowes, made for pulling up carpet-tacks.
Damn handy, like a miniature pry-bar with a screwdriver handle on one end.
I use it for prying on anything and everything (except pulling carpet tacks, which I never do).
It'd be perfect for that O2 sensor connector.


The engine mounts are up on the side of the engine just forward of the shock towers.
If you remove the wheel and pull back the plastic splash shield you'll see them.
They're large-ish with a a round center section with two mounting "feet".
I got a pair from Amazon, the maker was "Westar".
There are two separate part-numbers, one for driver's and the other for passenger side.



Thank you kindly Sir....
I'm always happy when I can make a small contribution here.
It was another 355 member who pointed me to the O2 and the MAP sensors, early this year.
That's what this place is for.
 

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There is a reason to replace both O2 sensors at the same time, but it isn't always necessary. Both of the O2 sensors deteriorate over a period of time and that can affect the signals sent to the ECM. The upstream sensor signal is the primary information that the ECM uses to determine fuel control when in closed loop (warmed up). If that signal is not accurate, it can affect fuel mileage. The downstream O2 sensor also provides a signal to the ECM. The ECM compares the readings from the upstream sensor to those from the downstream sensor, to determine catalytic efficiency. The reason for the recommendation to replace both at the same time is because if just the upstream one is changed, the downstream one may be deteriorated enough to cause the ECM to set a DTC for converter efficiency. So, if just the upstream O2 sensor is replaced and it doesn't result in a DTC, it probably isn't necessary to replace the downstream one. I haven't seen any evidence that a defective downstream O2 sensor will cause operational issues with the engine.
 

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MAP sensor:
Delphi # PS10002

[ame]http://www.amazon.com/Delphi-PS10002-Manifold-Absolute-Pressure/dp/B000CGK3ZY[/ame]
 

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Discussion Starter #15
Hi Rick, I just want to thank you for your inputs. Your diagnosis was spot on. I cleaned MAP, replaced the downstream O2 sensor and sprayed a lot of white grease on the engine mounts. I didn't expect by only replacing the downstream sensor would actually fix the problem. But man.....the rough idle was almost gone...I can barely feel it any more. I do feel like if I replace the upstream sensor, then it will be completely gone (could just be something in my head, haha). The truck idled a bit better after I cleaned MAP, then I did O2 and engine mount on the same day and now...the truck runs like new.

I am still trying to find a way to replace the upstream sensor though.
 

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Ricky Crew is on point!

I replaced both of my O2 sensors at 75k I was surprised how much smoother it was
 

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Discussion Starter #17
Ricky Crew is on point!

I replaced both of my O2 sensors at 75k I was surprised how much smoother it was
Now you make me want to replace the other sensor so badly.
 

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Hi Rick, I just want to thank you for your inputs. Your diagnosis was spot on. I cleaned MAP, replaced the downstream O2 sensor and sprayed a lot of white grease on the engine mounts. I didn't expect by only replacing the downstream sensor would actually fix the problem. But man.....the rough idle was almost gone...I can barely feel it any more. I do feel like if I replace the upstream sensor, then it will be completely gone (could just be something in my head, haha). The truck idled a bit better after I cleaned MAP, then I did O2 and engine mount on the same day and now...the truck runs like new.

I am still trying to find a way to replace the upstream sensor though.
I'm really happy to hear it!
As I posted though, I really can't take credit for those suggestions.
Another member here gave me the same advice (except for the engine mounts) about a year ago.
I feel guilty that I don't remember his name so I can give credit where it's due.

One thing though...
You metioned cleaning the MAP..
I suspect you mean the MAF (Mass Air Flow) sensor.

I was suggesting replacing the MAP (Manifold Air Pressure) sensor.
Cleaning the MAF is a good move, and should be done about every three months (?) or so.
The MAP can't really be cleaned, but it's cheap and very simple to replace.

Of the two, the MAP has more effect on idle smoothness, unless the MAF were just really, really dirty, in which case you would have worse problems than rough idle.

When spending the few bucks for a new MAP sensor is convenient, you really should go ahead and do so, in my opinion.

Glad to hear it's running well for you.
My truck continues to run and idle smooth as a baby's butt and I'm happy for that.
 

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Discussion Starter #19
I clean the MAF at every oil change so it's not dirty at all. I did clean the MAP, just sprayed electrical cleaner into the little hole there. I am not sure if it did anything because it's just a little film inside to form a vacuum space, but it did make the idle a bit better right after I cleaned it.
 
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