Altima hesistation off idle, revisited again!

One thing I forgot to mention in all this is that when I have a vacuum gauge
connected, the reading has a "vibration" to it. The vacuum is good and
strong (22 inches), but it swings back and forth maybe +/- 1 inch (as per
the scale on the gauge, not an actual inch) and does it about 6-8 times per
second. I just realized as I wrote the above that the tach has always had a
slight vibration to it at about the same speed as the vacuum gauge does.
Once I rev the engine off idle, the vibration goes away.

For all I know this is totally normal, but why it would only appear at idle
is a bit of a mystery to me.

On Sat, 15 Apr 2006 20:00:29 GMT, "JM" >
graced this newsgroup with:

>One thing I forgot to mention in all this is that when I have a vacuum gauge
>connected, the reading has a "vibration" to it. The vacuum is good and
>strong (22 inches), but it swings back and forth maybe +/- 1 inch (as per
>the scale on the gauge, not an actual inch) and does it about 6-8 times per
>second. I just realized as I wrote the above that the tach has always had a
>slight vibration to it at about the same speed as the vacuum gauge does.
>Once I rev the engine off idle, the vibration goes away.
>
>For all I know this is totally normal, but why it would only appear at idle
>is a bit of a mystery to me.
>


less air, poor air/fuel mixture. At idle it's just more noticeable.
When was the last time you cleaned the throttle body intake?

> wrote in message
...
> less air, poor air/fuel mixture. At idle it's just more noticeable.
> When was the last time you cleaned the throttle body intake?


Today, although admittedly it was only a quick job as it was threatening to
rain and I was almost out of throttle body cleaner. I have tried giving it
a thorough cleaning before using copious amount of cleaner and not had any
affect on things. Woudln't a (for example) leaking intake manifold gasket
on one cylinder cause this? Off idle or with the throttle open there would
be less vacuum behind the throttle plate so that might explain why it's less
apparent then.

But, there's no other evidence of such a leak...

On Sat, 15 Apr 2006 20:56:12 GMT, "JM" >
graced this newsgroup with:

> wrote in message
.. .
>> less air, poor air/fuel mixture. At idle it's just more noticeable.
>> When was the last time you cleaned the throttle body intake?
>
>
>Today, although admittedly it was only a quick job as it was threatening to
>rain and I was almost out of throttle body cleaner. I have tried giving it
>a thorough cleaning before using copious amount of cleaner and not had any
>affect on things. Woudln't a (for example) leaking intake manifold gasket
>on one cylinder cause this? Off idle or with the throttle open there would
>be less vacuum behind the throttle plate so that might explain why it's less
>apparent then.
>
>But, there's no other evidence of such a leak...
>


it's certainly possible that you've got an intake leak, one way to
find out is to use a spray bottle and spray a fine line of water
around the intake gaskets and see if the engine drops in idle.

I suspect though that it may be something like a dirty MAF or, the
throttle body is still dirty. The symptoms you mentioned still point
to that.

> wrote in message
...
>>But, there's no other evidence of such a leak...
> it's certainly possible that you've got an intake leak, one way to
> find out is to use a spray bottle and spray a fine line of water
> around the intake gaskets and see if the engine drops in idle.

I've tried that, only with TB cleaner, and had no change.

> I suspect though that it may be something like a dirty MAF or, the
> throttle body is still dirty. The symptoms you mentioned still point
> to that.

Well, the MAF does respond to airflow according to my meter, so I think
that's doing its job; can you suggest any other ways of cleaning the TB that
might get better results? In the past I've cleaned the ridge of carbon off
around the throttle plate, and sprayed TB cleaner into the open intake,
which usually results in some black smoke out the exhaust once the car
starts, but other than that and spraying directly into a vacuum line, I
don't know what else to attack.

I'd like to get the idle control motor out and clean its seat and pintle but
it's just about impossible to get to. I have disconnected its air supply
tube from the intake hose though and shot some cleaner in there.

On Sat, 15 Apr 2006 22:08:23 GMT, "JM" >
graced this newsgroup with:

>
> wrote in message
.. .
>>>But, there's no other evidence of such a leak...
>> it's certainly possible that you've got an intake leak, one way to
>> find out is to use a spray bottle and spray a fine line of water
>> around the intake gaskets and see if the engine drops in idle.
>
>I've tried that, only with TB cleaner, and had no change.

hmmm...

>
>> I suspect though that it may be something like a dirty MAF or, the
>> throttle body is still dirty. The symptoms you mentioned still point
>> to that.
>
>Well, the MAF does respond to airflow according to my meter, so I think
>that's doing its job; can you suggest any other ways of cleaning the TB that
>might get better results? In the past I've cleaned the ridge of carbon off
>around the throttle plate, and sprayed TB cleaner into the open intake,
>which usually results in some black smoke out the exhaust once the car
>starts, but other than that and spraying directly into a vacuum line, I
>don't know what else to attack.

...the most cost efficient way is that way you've cleaned it. The only
other way is a complete tear down and that's WAY more of a PITA than
you'd want to get into.

>
>I'd like to get the idle control motor out and clean its seat and pintle but
>it's just about impossible to get to. I have disconnected its air supply
>tube from the intake hose though and shot some cleaner in there.
>

If the control motor was bad (or going bad), it probably wouldn't hold
an idle at all. Another possibility is that you've got either a bad
injector or hopefully, just dirty injectors. Have you tried a botlle
of BG-44K? It just may need a good injector cleaning.

There's nothing worse than hunt and peck and that's what it sounds
like you're doing now. If the BG-44K doesn't help, then I'd have some
diagnostics run on it. You may have an ignition problem.

JM wrote:

>
> I'd like to get the idle control motor out and clean its seat and pintle but
> it's just about impossible to get to. I have disconnected its air supply
> tube from the intake hose though and shot some cleaner in there.

I don't think the throttle body has much to do with the flutter in the
vacuum, if that is what you are thinking. The flutter is probably due to
a sticking or burnt valve. It disappears at higher RPM simply because
your gauge can't move fast enough to see it at anything above an idle.

-jim

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On Sat, 15 Apr 2006 17:37:32 -0500, jim >
graced this newsgroup with:

>
>
>JM wrote:
>
>>
>> I'd like to get the idle control motor out and clean its seat and pintle but
>> it's just about impossible to get to. I have disconnected its air supply
>> tube from the intake hose though and shot some cleaner in there.
>
>I don't think the throttle body has much to do with the flutter in the
>vacuum, if that is what you are thinking. The flutter is probably due to
>a sticking or burnt valve. It disappears at higher RPM simply because
>your gauge can't move fast enough to see it at anything above an idle.
>
>-jim
>


go point. It could be ignition related as well. Personally, if some
quick, cheap fixes don't correct the problem, IMHO, I'd stop wasting
time and money and get it professionally diagnosed.

"jim" > wrote in message
...
> I don't think the throttle body has much to do with the flutter in the
> vacuum, if that is what you are thinking. The flutter is probably due to
> a sticking or burnt valve. It disappears at higher RPM simply because
> your gauge can't move fast enough to see it at anything above an idle.

What about a valve out of adjustment? It would have to be rediculously out
I suppose? The car has always had a tapping at startup on warmer days that
I've always suspected was a valve, but the dealer's opinion is that it's
probably a hairline crack in the exhaust manifold since these valves rarely
need adjusting and it's apprently a lot of work to adjust them. The engine
uses shim adjusted, directly actuated valves; is it still possible one is
sticking or not closing fully?

If a valve was stuck fully open I'd expect to have a dead cylinder with no
compression -- would a cylinder with a burnt valve, etc. show lower
compression?

Would you expect a burnt/sticking/misadjusted valve to cause the hesitation
also?

My spark plug hole seals are starting to leak now, so I may just have to
pull the valve cover to replace them in the near future. Maybe I'll also
see what I can see as far as the valves go at the same time.

Thanks for the suggestions,

JM wrote:
> Ok, so I'm still trying to figure out my hesitation off idle in my 1999
> Altima.
>
> I've checked for vacuum leaks and I'm relatively sure there are none.
> I've checked the fuel pressure, and it's within spec. The regulator behaves
> as described in the service manual when I disconnect the vacuum line.
> I tested the MAF sensor and its output voltage rises smoothly with any
> increase in throttle opening.
> I tested the TPS and it operates smoothly and is within spec.
> The coolant temp sensor and intake air temp sensor both are about right
> according to the service manual.
> It has clean plugs, newish rotor, cap, and wires, and is not burning oil or
> coolant.
>
> There are no trouble codes stored, and aside from this problem and having a
> slightly high idle, the car runs smoothly and has good power at all other
> revs.
>
> The problem manifests itself as a drop in revs/stumble when I tap the
> throttle off idle. It's most obvious with small abrupt throttle openings,
> the kind you would use to take off from a stop (it's a manual trans).
> It's more severe when the car has been started between 5 and 10 minutes of
> having been shut of and is still warm. With a shorter or longer stop, it
> doesn't tend to be any worse than normal.
>
> I tested the O2 sensor as well as I could with the tools I have; my analog
> meter's lowest range is 10V, so it's hard to accurately monitor the sensor
> with it, and my digital meter I suspect is a bit slow to show the voltage
> changes from the sensor. But, with the digtal meter, the voltage seemed to
> settle around .2 volts at idle, and would spike up to around .7 if I revved
> the engine. I measured the resistance of pins 1 and 3 (the heater element I
> suspect) of the sensor, as per the service manual's instruction, and it
> reads almost 8 ohms hot, and 4.6 ohms or so at around 5 degrees C.
>
> The service manual says it should fall between 2.3 and 4.3 ohms at 25 deg.
> C, so I assume the idea is the resistance increases with temperature. If
> that's the case, then at 25C, I would expect the resistance to be more than
> 4.6 ohms as I recorded at 5 degrees, so that is somewhat suspect.
>
> I priced a new sensor at around $100 CDN today from the dealer, so I'm half
> tempted to install one. If it doesn't fix the problem at least it will be
> new and might help my fuel economy a little although it isn't poor to begin
> with.
>
> Any thoughts/suggestions as to what else I might look at?
===========
===========
Classification:
HA98-005

Reference:
NTB99-006

Date:
March 15, 1999

1998-99 ALTIMA, MIL "ON" AND/OR POOR DRIVEABILITY DUE TO A/C EVAPORATOR
CONDENSATION LEAKING ON ECM

APPLIED VEHICLES:
All 1998-99 Altima (L30)

SERVICE INFORMATION

If a 1998-99 Altima exhibits a MIL "ON" and/or poor driveability such
as engine hesitation or no starting, the cause may be air conditioning
(A/C) evaporator condensation leaking onto the engine control module
(ECM). Air conditioning condensation can accumulate and leak onto the
ECM if the A/C evaporator drain tube becomes blocked by debris such as
leaves, insect nests, etc.




just a thought.