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1999 Altima misses off idle



 
 
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  #1  
Old March 12th 06, 06:33 PM posted to rec.autos.tech
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Default 1999 Altima misses off idle

Hi group,

I've got a 1999 Altima with 100,000 kms. Ever since I got it almost 2
years ago, it's had a slightly too high idle (varies, but around 850-900
rpm) and it also has a stumble off idle. The idle itself is more or
less smooth, although if I listen at the end of the exhaust it does seem
slightly irregular, but not by too much.

If I punch the throttle while it's idling, especially when it's just
been started (warm or cold) or before it's warmed up first thing in the
morning, it'll stumble for a second or so (the whole engine shakes), and
then rev up as expected.

When I do this, as soon as I open the throttle I can hear a sucking
sound from the end of the intake, and I can hear the injectors speed up
quite a bit, but it's not until almost a second has gone by that the
engine actually revs.

If I am less abrupt with the throttle, it'll rev just fine, and if I
punch the gas when it's up around 1500-2000 RPM, there's no noticeable
hesitation.

After the car's warmed up, the severity and delay decrease a fair bit,
but they're still noticeable.

I've always suspected a vacuum leak, but today I went out and
disconnected the intake tube from the MAF sensor, sealed it off with a
plastic bag, and then tried blowing into the tube that runs off to the
idle control valve. My plastic bag inflated slightly, but there was no
obvious leakage from anywhere except a very slight and very slow hissing
from around the EGR valve area that I wouldn't expect would affect anything.

I then tried unplugging the coolant temp sensor. This caused the idle
to be even higher, and amplified the hesitation off idle quite a bit. I
know this is no way to make a diagnosis, but it seems suspicious to me.

I had it to the dealer last fall, and everything checked out okay -- the
TPS was within spec and the idle control motor was at 30% which
apparently is normal.

In the past I've checked the throttle position sensor and MAF sensor
ground, and both were fine, and I've replaced the plugs, wires, dist.
cap and rotor within the last few years. I have tested the coolant temp
sensor a few times and it did seem to change from hot to cold, but it's
hard to get at with my multimeter leads and I wonder if it may be out of
spec just enough to cause my particular problem but nothing more severe
than that.

Can anyone suggest what else I should look at? I hear the coolant
sensors are pretty common to go bad, and not too expensive, maybe I'll
price one and swap it out just to cross one more thing off the list.

Thanks in advance for any help.1
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  #2  
Old March 12th 06, 07:31 PM posted to rec.autos.tech
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Default 1999 Altima misses off idle

1st check for trouble codes!
My guess is either an EGR valve malfunction or perhaps egr valve ports are
clogged with carbon!

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"JM" > wrote in message
...
> Hi group,
>
> I've got a 1999 Altima with 100,000 kms. Ever since I got it almost 2
> years ago, it's had a slightly too high idle (varies, but around 850-900
> rpm) and it also has a stumble off idle. The idle itself is more or
> less smooth, although if I listen at the end of the exhaust it does seem
> slightly irregular, but not by too much.
>
> If I punch the throttle while it's idling, especially when it's just
> been started (warm or cold) or before it's warmed up first thing in the
> morning, it'll stumble for a second or so (the whole engine shakes), and
> then rev up as expected.
>
> When I do this, as soon as I open the throttle I can hear a sucking
> sound from the end of the intake, and I can hear the injectors speed up
> quite a bit, but it's not until almost a second has gone by that the
> engine actually revs.
>
> If I am less abrupt with the throttle, it'll rev just fine, and if I
> punch the gas when it's up around 1500-2000 RPM, there's no noticeable
> hesitation.
>
> After the car's warmed up, the severity and delay decrease a fair bit,
> but they're still noticeable.
>
> I've always suspected a vacuum leak, but today I went out and
> disconnected the intake tube from the MAF sensor, sealed it off with a
> plastic bag, and then tried blowing into the tube that runs off to the
> idle control valve. My plastic bag inflated slightly, but there was no
> obvious leakage from anywhere except a very slight and very slow hissing
> from around the EGR valve area that I wouldn't expect would affect

anything.
>
> I then tried unplugging the coolant temp sensor. This caused the idle
> to be even higher, and amplified the hesitation off idle quite a bit. I
> know this is no way to make a diagnosis, but it seems suspicious to me.
>
> I had it to the dealer last fall, and everything checked out okay -- the
> TPS was within spec and the idle control motor was at 30% which
> apparently is normal.
>
> In the past I've checked the throttle position sensor and MAF sensor
> ground, and both were fine, and I've replaced the plugs, wires, dist.
> cap and rotor within the last few years. I have tested the coolant temp
> sensor a few times and it did seem to change from hot to cold, but it's
> hard to get at with my multimeter leads and I wonder if it may be out of
> spec just enough to cause my particular problem but nothing more severe
> than that.
>
> Can anyone suggest what else I should look at? I hear the coolant
> sensors are pretty common to go bad, and not too expensive, maybe I'll
> price one and swap it out just to cross one more thing off the list.
>
> Thanks in advance for any help.1



  #3  
Old March 12th 06, 08:06 PM posted to rec.autos.tech
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Default 1999 Altima misses off idle

Backbone wrote:
> 1st check for trouble codes!
> My guess is either an EGR valve malfunction or perhaps egr valve ports are
> clogged with carbon!
>

Forgot to mention, no codes set, and I cleaned the EGR and ports when I
got the car (had the problem then also). Also, if I pull the vacuum
line to the EGR valve, effectively disabling it, there's no change. It
does feel like that kind of a problem though
  #4  
Old March 12th 06, 08:29 PM posted to rec.autos.tech
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Default 1999 Altima misses off idle


JM wrote:
> Backbone wrote:
> > 1st check for trouble codes!
> > My guess is either an EGR valve malfunction or perhaps egr valve ports are
> > clogged with carbon!
> >

> Forgot to mention, no codes set, and I cleaned the EGR and ports when I
> got the car (had the problem then also). Also, if I pull the vacuum
> line to the EGR valve, effectively disabling it, there's no change. It
> does feel like that kind of a problem though


If I had it I would look at fuel trim with a scantool, under many
different driving conditions. If fuel trim was too far off I would
suspect dirty MAF sensor elements first. I suppose that you have
checked the integrity of the large intake hose (splits, cracks, fit)?

Toyota MDT in MO

  #5  
Old March 12th 06, 09:02 PM posted to rec.autos.tech
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Default 1999 Altima misses off idle

Comboverfish wrote:
>> Forgot to mention, no codes set, and I cleaned the EGR and ports when I
>> got the car (had the problem then also). Also, if I pull the vacuum
>> line to the EGR valve, effectively disabling it, there's no change. It
>> does feel like that kind of a problem though

> If I had it I would look at fuel trim with a scantool, under many
> different driving conditions. If fuel trim was too far off I would
> suspect dirty MAF sensor elements first. I suppose that you have
> checked the integrity of the large intake hose (splits, cracks, fit)?


Yes, I've been over that hose and the various ones that branch off of it
a few times, and everything seems in order. I don't have a tool that
will let me see the trim values but I'll keep that in mind in case I do
take it somewhere for another look.

Thanks.
  #6  
Old March 12th 06, 11:34 PM posted to rec.autos.tech
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Default 1999 Altima misses off idle

JM wrote:
> Comboverfish wrote:
>>> Forgot to mention, no codes set, and I cleaned the EGR and ports when I
>>> got the car (had the problem then also). Also, if I pull the vacuum
>>> line to the EGR valve, effectively disabling it, there's no change. It
>>> does feel like that kind of a problem though

>> If I had it I would look at fuel trim with a scantool, under many
>> different driving conditions. If fuel trim was too far off I would
>> suspect dirty MAF sensor elements first. I suppose that you have
>> checked the integrity of the large intake hose (splits, cracks, fit)?

> Yes, I've been over that hose and the various ones that branch off of it
> a few times, and everything seems in order. I don't have a tool that
> will let me see the trim values but I'll keep that in mind in case I do
> take it somewhere for another look.


I was out today and noticed there is a distinct hissing sound when I rev
the engine coming from somewhere around the EGR valve or possibly the
intake manifold. I know this particular year Altima was known for the
intake manifold gasket breaking down and leaking, but this sounds like
it's closer to the firewall than that.

I went over all the vacuum lines I could see and they all look good, so
I'm a little puzzled where this sound is coming from. I have tried
shooting throttle body cleaner where the manifold bolts to the head,
with no change in idle, and I also sprayed around the various metal bits
of vacuum line, but this had no effect.

I'm half hoping I'm on to something though...
  #7  
Old March 13th 06, 04:06 AM posted to rec.autos.tech
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Default 1999 Altima misses off idle


JM wrote:
> JM wrote:
> > Comboverfish wrote:
> >>> Forgot to mention, no codes set, and I cleaned the EGR and ports when I
> >>> got the car (had the problem then also). Also, if I pull the vacuum
> >>> line to the EGR valve, effectively disabling it, there's no change. It
> >>> does feel like that kind of a problem though
> >> If I had it I would look at fuel trim with a scantool, under many
> >> different driving conditions. If fuel trim was too far off I would
> >> suspect dirty MAF sensor elements first. I suppose that you have
> >> checked the integrity of the large intake hose (splits, cracks, fit)?

> > Yes, I've been over that hose and the various ones that branch off of it
> > a few times, and everything seems in order. I don't have a tool that
> > will let me see the trim values but I'll keep that in mind in case I do
> > take it somewhere for another look.

>
> I was out today and noticed there is a distinct hissing sound when I rev
> the engine coming from somewhere around the EGR valve or possibly the
> intake manifold. I know this particular year Altima was known for the
> intake manifold gasket breaking down and leaking, but this sounds like
> it's closer to the firewall than that.
>
> I went over all the vacuum lines I could see and they all look good, so
> I'm a little puzzled where this sound is coming from. I have tried
> shooting throttle body cleaner where the manifold bolts to the head,
> with no change in idle, and I also sprayed around the various metal bits
> of vacuum line, but this had no effect.
>
> I'm half hoping I'm on to something though...


You may just be paying more attention to the sound of the idle speed
control than normal. As it opens up (revving the engine up and down
will cause this) more air will rush through the intake tube and cause a
sound like you describe. Unplug the ISC connector and try again. See
if this is the noise you are chasing.

Toyota MDT in MO

  #8  
Old March 13th 06, 11:41 PM posted to rec.autos.tech
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Default 1999 Altima misses off idle

Comboverfish wrote:
> You may just be paying more attention to the sound of the idle speed
> control than normal. As it opens up (revving the engine up and down
> will cause this) more air will rush through the intake tube and cause a
> sound like you describe. Unplug the ISC connector and try again. See
> if this is the noise you are chasing.


Actually I had the TPS unplugged at the time, which stops the ECU from
opening the idle control valve, so it wasn't coming into play. I'm
familiar with the hissing sound the IACV (Nissan's terminology) makes
though, and this is different. It was a short, sharp hiss that
corresponded with the suck sound from the end of the intake. I wondered
if I was just hearing air rushing inside the manifold, but when I put my
rubber listening hose up against the manifold, the sound was less audible.

I did later listen for the sound again with the TPS connected and the
IACV operating normally, and it was still there, but much less apparent.
I suspect this is because the IACV was opening and moderating the
demand for so much air all at once.

I just wish I could pinpoint where the sound is coming from a little better.


  #9  
Old March 14th 06, 06:45 AM posted to rec.autos.tech
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Default 1999 Altima misses off idle

On Mon, 13 Mar 2006 21:46:57 -0800 "Backbone" > wrote:
> "JM" > wrote in message
>
> > I just wish I could pinpoint where the sound is coming from a little

> better.
>
> <smiles> I use a very long screwdriver. Use the handle as the listening
> device, the tip as the probe. Listen as you touch the probe to various
> locations - It'll be apparent as to the sounds exact location.


For $15, you can get a mechanic's stethoscope
at Sears (or most any auto parts), which I
find to be better than a screwdriver.

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  #10  
Old March 14th 06, 06:46 AM posted to rec.autos.tech
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Default 1999 Altima misses off idle

"JM" > wrote in message
...


> I just wish I could pinpoint where the sound is coming from a little

better.

<smiles> I use a very long screwdriver. Use the handle as the listening
device, the tip as the probe. Listen as you touch the probe to various
locations - It'll be apparent as to the sounds exact location.

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