Weird Idle Speed Problem

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jcb - 14 Jan 2008 17:22 GMT

Hello experts,
I ran into a weird idle speed problem on my '02 Nissan Sentra SE-R
(QR25 engine, 5-speed M/T).
After about an hour of hwy driving (~60mph), I noticed that the idle
speed was up around 1200 rpm when I stopped at a traffic light.
Shortly after got home, while the car is still at normal operation
temperature, I performed the "Idle speed learning" procedure (I'm sure
I did everything correctly, because I've done that before); however,
at this time, instead of having the idle speed drops to
~750rpm, during the learning stage, the engine sets the idle speed up
exactly at 1500rpm.
I've repeated the idle speed leaning steps few times, but every time,
it just sets to 1500rmp (btw, I read this number from the Scan tool
and there is no MIL light on. ECU doesn't sense any error)
I ran out of ideas. Any hints would be much appreciated.

Have a nice day

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Jim Yanik - 14 Jan 2008 20:57 GMT

jcb <mail.jun.l@gmail.com> wrote in news:a7733402-c7c7-4fa1-9e1c-
980af78b5df4@21g2000hsj.googlegroups.com:

> Hello experts,
> I ran into a weird idle speed problem on my '02 Nissan Sentra SE-R
[quoted text clipped - 13 lines]
>
> Have a nice day

I'm no expert....but

I have a similar problem with my 03 SE-R SpecV.the idle increased to ~1500-
2000 rpm,drifted around,and soon enough,set the MIL light with an error
code of P0507(too fast an idle speed).I had to go thru the idle set
procedure,too.
Eventually,the code cleared itself(MIL went out),it took quite a long
time,though.
my idle has been pretty stable recently.One thing that bothers me is the
long time it takes for the RPMs to drop back after I get off the gas pedal.

there's a tech bulletin out on the power steering pressure switch going
intermittent,causing idle problems.
the switch normally tells the ECU to increase the idle when the steering is
moved,to keep from stalling.

this site is a big help;
http://www.nissanhelp.com/

you can download parts of the factory manual,one DL per 24hr period.
They list all the bulletins for each Nissan model.

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Jim Yanik
jyanik
at
kua.net

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jcb - 15 Jan 2008 19:57 GMT

> jcb <mail.jun.l@gmail.com> wrote in news:a7733402-c7c7-4fa1-9e1c-
> 980af78b5df4@21g2000hsj.googlegroups.com:
[quoted text clipped - 45 lines]
>
> - Show quoted text -

Thank you Jim for the quick reply...
I've done some research before posting this msg, so I am aware of the
website you mentioned. I am not sure my issue is the same as the PSP
switch, because while idling, if I turn the steering wheel, I saw the
idle speed changes (by dropping a bit and then jumping back to
~1200rpm again), which means that the ECU receives the feedback from
the PSP switch and reacted accordingly. If the PSP switch is failed as
the bulletin described, then it should be always "ON" and there
shouldn't be any changes while tuning the steering wheel.
I'm not really a mechanical savvy guy, so I'm not sure my analysis
makes sense or not.
I found another website saying that it could be "Idle Airflow
Controller" problem, but I haven't checked it out yet. I'll update the
group once I figured out what the real issue is...

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Jim Yanik - 15 Jan 2008 23:33 GMT

>> jcb <mail.jun.l@gmail.com> wrote in news:a7733402-c7c7-4fa1-9e1c-
>> 980af78b5df4@21g2000hsj.googlegroups.com:
[quoted text clipped - 56 lines]
> the bulletin described, then it should be always "ON" and there
> shouldn't be any changes while tuning the steering wheel.

In my case,I suspect the PSP switch is sticking intermittently.

> I'm not really a mechanical savvy guy, so I'm not sure my analysis
> makes sense or not.
> I found another website saying that it could be "Idle Airflow
> Controller" problem, but I haven't checked it out yet. I'll update the
> group once I figured out what the real issue is...

I don't think our model years(2002 and newer) have an idle air controller.I
believe it's all controlled by the electronic throttle control.That's why
you have to use a "procedure" to set the idle.

Perhaps it's just the throttle body gummed up and needs cleaning.(SWAG)

Ther's a recall on the ECU for my 03,I'm not sure if it covers your year
too,but it is something about stalling(IDLE PROB?) and involves a
reprogramming of the ECU. I may get that reprogramming done.

Maybe that would solve your problem,although I'd try cleaning the throttle
body first.

Signature

Jim Yanik
jyanik
at
kua.net

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jcb - 17 Jan 2008 05:36 GMT

> >> jcb <mail.ju...@gmail.com> wrote in news:a7733402-c7c7-4fa1-9e1c-
> >> 980af78b5...@21g2000hsj.googlegroups.com:
[quoted text clipped - 85 lines]
>
> - Show quoted text -

Hi Jim and folks,
Just wanted to give you all an update... Unfortunately, I'm still not
able to figure out what the problem was, but fortunately, the problem
is gone ;-)
This may be even more scary because who knows when it'll come back
again. Anyway here is what I've done...
I know it's essentially an air/fuel ratio problem, so started to trace
done from the air intake end. I opened the air filter box and
discovered that the air filter was kind of dirty and a bit of smoky
too, so I replaced it with a new one.
Then I tied up all connectors around the throttle area, as well as
both O2 sensor connectors. I didn't expect any magic could happen by
doing these, but after I drove the car to work, I performed the Idle
Leaning Procedure one more time, while the car was warm.
May be my persistent touched the heart of my car (I've done this
learning procedure so many times since the problem occurred), or may
be your great support created a miracle, the re-learning steps
actually worked this time. The idle speed was set back to ~700rpm and
still there since then.
Now my car runs perfectly (very quiet, smooth and powerful), but sadly
I don't know which specific thing that I've done fixed the problem.
Anyway, life is back to normal... I may bother you guys later when the
problem comes back.
Have a nice day...

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JM - 15 Jan 2008 22:39 GMT

> Hello experts,
> I ran into a weird idle speed problem on my '02 Nissan Sentra SE-R
[quoted text clipped - 11 lines]
> and there is no MIL light on. ECU doesn't sense any error)
> I ran out of ideas. Any hints would be much appreciated.

I had the same kind of problem with my '99 Altima. When I bought it it
idled close to 1000 rpm all the time, and it liked to want to rev up and
hang there for a little bit whenever I came to a stop and pushed in the
clutch. I couldn't adjust the throttle speed because the adjust screw was
seized, but I eventually replaced it and was able to adjust the idle down,
but I had to turn the screw all the way to get it close to 750rpm. I still
had the issue of it wanting to rev up when I came to a stop however.

I also noticed that when in the idle adjust mode (with TPS disconnected) my
revs were higher than with the TPS connected normally, as if the ECU was
already compensating for the high idle but in adjust mode I was seeing the
true scale of the problem.. Anyway I unfortunately didn't find the cause of
the problem, but I thought I'd throw this (small) bit of info out there in
case it helps at all.
I checked for any codes, and didn't find any, tested the TPS with no
problems, replaced the coolant temp sensor with no change, verified the MAF
output as well as I could. I always wondered if I had some air in the
cooling system that was affecting the coolant temp sensor, but never did
disprove that one.

I've seen a few posts of similar issues, mostly with Sentras for some
reason, but I never saw a followup with what the solution was...

Anyway I hope you find the problem, let us know if you do -- I sold the car
to my dad so I can pass that on to him.

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Jim Yanik - 15 Jan 2008 23:43 GMT

> .
>> Hello experts,
[quoted text clipped - 14 lines]
>
> I had the same kind of problem with my '99 Altima. When I bought it

"pre-owned" or new?

> it idled close to 1000 rpm all the time, and it liked to want to rev
> up and hang there for a little bit whenever I came to a stop and
> pushed in the clutch. I couldn't adjust the throttle speed because
> the adjust screw was seized, but I eventually replaced it and was able
> to adjust the idle down, but I had to turn the screw all the way to
> get it close to 750rpm.

No idle speed screw on the 2000(Sentra) and newer QR25DE motors.It's all
done by the ECU.

> I still had the issue of it wanting to rev up
> when I came to a stop however.
[quoted text clipped - 16 lines]
> Anyway I hope you find the problem, let us know if you do -- I sold
> the car to my dad so I can pass that on to him.

Perhaps a sticking idle air controller valve? (IACV)
It's on one end of the intake manifold,opposite from the throttle body.
my Haynes book says it can suffer from excess carbon deposits.

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Jim Yanik
jyanik
at
kua.net

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