Low/rough idle needle doesn't jump truck doesn't die

[Cameron23]

The needle stays here, doesn't jump around like its fighting to stay alive, the truck doesn't die, but it kinda feels like it's going to. Definitely feels rougher than normal when in drive and stopped at a light, while truck kinda shakes while stopped, no codes.


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[Cameron23]

Bump


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[Cameron23]

Nothing really to capture on video, the needle stays at just around what I assume is 550. The whole truck kinda mildly shakes like its gonna stall out but it doesn't. Right when I come to a stop the needle is at like 750 then it drops down after about 2 seconds. Drives fine, it's just the idle that's got me worried.


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[TheFauxFox]

Fuel Filter/Pump
Distributor
Timing

Thats what I want to say first.

 

[Cameron23]

Timing belt was replaced by Nissan within 25k miles

And fuel pump/filter is a ***** isn't it?



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[Muadeeb]

The pump sucks; you'll have to drain and drop the tank to do that. The filter will just pee all over you when you change it.

 

[Cameron23]

How hard is it to do? Is there a write up?


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[TheFauxFox]

How hard is it to do? Is there a write up?

I can't find the writeup posted a year or so ago. Here is one from XF:
http://xterrafirma.com/content/replacing-fuel-filter

It is quite simple. The part is common for auto part stores and should cost ~$20 or less.

 

[Cruecible]

The filter is cake. Getting the hose off the filter can be a real PITA though. I got a tool that's made to separate hoses off nozzles from Harbor Freight for like $3. It made it much easier.

You could also try the good ol' Seafoam routine. May help clear some crap out too

 

[Cameron23]

Okay I have a pending code P0325.
Light didn't come on, I just had AutoZone check and that's what came up.

What now?


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[Muadeeb]

Knock sensor. Kinda a duh with these problems, ignored otherwise

 

[Cameron23]

Knock sensor. Kinda a duh with these problems, ignored otherwise

So should I replace my knock sensor? Maybe it's causing the problems by retarding the idle?


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[02Xterra]

Knock sensor doesn't have that big of an effect on the n/a 3.3's


I just went thru something identical to this a few weeks ago.. while it's running can you smell fuel? Like its running rich. Mine was doing that.. did some research and found that the fuel pressure regulator, which is under in intake plenum and bolted to the fuel rail, can develop a hole in the diaphragm, causing extra fuel to dump into the #6 cylinder. So on a sunday I replaced the FPR and the #6 plug, reinstalled in intake plenum and fired it up.. and it ran the same.. so I drove around for 15 minutes or so to get it up to temp.. no change. I don't DD the X anymore so on monday after work I was on the way to a buddies shop to get him to plug in their scanner and run some tests. On the way there i stopped at a red light and noticed that it was idling perfect. I couldn't believe it! My buddy and I discussed it when I got there and best we can figure is that since the FPR was dumping extra fuel into the #6 cylinder, it couldn't burn it off so it went right out of the exhaust, which messed with the O2 sensors. But after driving for a while the computer realizes the conditions have changed and starts to relearn and adjust. I bet if I had driven around for longer that sunday the X would have started running better.

What I did: Pulled the fuel pump fuse and tried to start the X a few times, this releases the fuel pressure in the lines; drained the coolant, removed intake plenum, replaced fuel pressure regulator, replaced #6 spark plug, reinstalled intake plenum, and drove around for a while. It has been running fine ever since

 

[Cameron23]

I haven't smelt any huge odor of fuel. But it's worth a try. I'm going to remove the intake plenum anyway to get access to the knock sensor. Is there anyway to visually check the FPR or a way to figure out if it's faulty?


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[02Xterra]

For the time it takes to change that, I honestly wouldn't bother with the knock sensor.. mines been throwing the code for 7 years lol. I believe there's a procedure in the FSM for testing the fpr.. but one check would be to see if there's fuel in the vacuum line connection to the fpr.. that would mean the diaphragm has a hole and is letting gas thru

 

[Cameron23]

Will replacing the knock sensor stop the code from being present? Also, do you have pictures of your repair? What was the cost?

explain the vacuum line diagnosis to me. Why would there be fuel in the line? Can I check that with the manifold on?


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[Muadeeb]

yes, probably. But the code doesn't set the CEL so isn't worth the hassle in removing the lower intake to deal with it.

 

[Cameron23]

So any other ideas before I pull the intake plenum to check out the fuel pressure regulator in 2 weeks?


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[Cameron23]

Boomp


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[Cameron23]

Bump


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[Prime]

Sounds like a solid plan to me. Emplacement the FPR, and I'd do the fuel filter while you're at it.

 

[Prime]

And go ahead and do a tune-up since you'll have the intake off and the spark plugs will be easy to get to.

 

[Cameron23]

How hard is it to get the lower plenum off? I've done the upper to change my valve cover gasket but not the lower.


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[Cameron23]

Bump


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[Cruecible]

When I was having all the problems with mine when I first bought it, and after breaking down and taking it to a mechanic after doing every DIY I could, he plugged in a handheld diagnostic reader and figured out the problem in a matter of minutes. He wasn't a self-professed Xterra or Nissan master mechanic, but just by reading and watching the diagnostic data on the reader, he was able to pinpoint where the problem was by noticing fluctuating readings from the O2 sensors.

Having the codes pulled at Autozone or places like that may help point you in the right general direction as it did for me, but having a good honest mechanic plug in a diagnostic reader and taking a look at it really was worth it. It could save you a lot of time and money in the long run.

 

[Cameron23]

Changed the fuel filter, no change in problem. And sweet baby Jesus there was fuel everywhere! Even after doing the fuel pump fuse thing. But I'll be putting it into McCarthy Nissan in Olathe to diagnose in about 2 weeks when I get paid.


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[Prime]

Did you get to the FPR yet?

 

[Cameron23]

Did you get to the FPR yet?

I want them to tell me what the problem is before I pull the lower plenum. Or at least give me data and readings when it is doing the crappy idle that way I can better diagnose or they can diagnose it for me.


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[02Xterra]

You don't need to remove the lower plenum. The fpr is under the upper intake plenum.

I agree with having it diagnosed first tho, that way you can get a clear idea of what's going on

 

[Cameron23]

Oh I've gotten that off to change the valve cover gasket. Okay well that cuts the intimidation factor in half


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[02Xterra]

Yea man it's not bad to get to! Sorry for the delay, here's where it is! Just to the right of the last intake port

 

[Cameron23]

This what we're talking about?


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[Prime]

Yes. That's it.

 

[Cameron23]

Cool maybe I'll tackle it on a weekend then and replace it even if not necessary. I just don't have the cash to put it in the shop right now with no idea what it will end up being. Maybe at the end of the month of the problem isn't fixed yet.


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[Cameron23]

Well I came home from a mission trip and started up the Xterra which had been sitting for a week. As soon as it started it almost died. It dropped to ~25 rpm then saved itself and idled (poorly) at 300 rpms so I took it in. Turned out I had a cracked exhaust manifold and multiple cylinder misfires and a bad S0 sensor. I had them replace the exhaust manifold and sensor and they ordered the stuff for an injector and spark plug replacement for cylinder 3 which will be done on Monday before I take it to the lake. But there goes 1,400 bucks. Which I know is highway robbery but I didn't have much of a choice as I need my car for the rest of the summer every day.

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