Rough Idle, running - Stepper motor? O2 Sensor?

Hello All,

Over the past year or two, the "Check Engine" (EFI) light in my '93
Range Rover 4.2 has occasionally come on while idling. Sometimes this
comes with a rough idle, sometimes not. In the past, I have simply
reset it by pulling the negative lead from the battery and all is well
for at least several weeks. The first time it did this, I took it to
my mechanic who put it on the test book and it came back with an "idle
too slow" reading. At the time, he said it must be the stepper motor
and that I should change it if it gets bad.

OK, when this happened most recently, the rough idle didn't go away
and in fact yielded some occasionally coughing when the RR was under
strain. However, when the check engine light came on the whole system
immediately reverted to normal smooth running and stayed that way
until I reset the system.

I assumed that the stepper motor had finally completely gone and
replaced it this evening. Things seemed a little better but still, the
idle was a bit rough and it seemed a but underpowered when under
strain going up a steep hill. Then, after a half an hour, the check
engine light came back on and, like clockwork the engine was running
perfectly and able to take the steepest of hills with aplume.

Sooooooooo....Now I'm guessing that BOTH the stepper motor and a
sensor like the O2 sensor were bad. Replacing the stepper motor DID
improve things. However, when the check engine light it coming on, it
seems that the system is ignoring some bad input somewhere and that
makes me suspect a sensor.

Am I on the right track? Does this make any sense at all? Any ideas
will be appreciated. This Rover is a stalwart beast that has given
me very little trouble in the past and my heart tells me that it is
something minor - please, let it be so!

Thanks,

Arden
1993 Range Rover County LWB (Vogue LSE)

Success!

Thanks for all the (ahem) help.

The new stepper motor did improve things as noted. However, what
REALLY did the trick was cleaning all the contacts for the airflow
meter, the coolant temperature sensor and the throttle position sensor
with an old toothbrush and applying dielectric grease.

Did that... and it all was as smooth as silk and the "Check Engine"
(EFI) light has stayed off.

Woo Hoo!

Arden
1993 Range Rover County LWB (Vogue LSE)



On Tue, 01 Nov 2005 17:43:04 -0800, Arden <[email protected]> wrote:

>
>Hello All,
>
>Over the past year or two, the "Check Engine" (EFI) light in my '93
>Range Rover 4.2 has occasionally come on while idling. Sometimes this
>comes with a rough idle, sometimes not. In the past, I have simply
>reset it by pulling the negative lead from the battery and all is well
>for at least several weeks. The first time it did this, I took it to
>my mechanic who put it on the test book and it came back with an "idle
>too slow" reading. At the time, he said it must be the stepper motor
>and that I should change it if it gets bad.
>
>OK, when this happened most recently, the rough idle didn't go away
>and in fact yielded some occasionally coughing when the RR was under
>strain. However, when the check engine light came on the whole system
>immediately reverted to normal smooth running and stayed that way
>until I reset the system.
>
>I assumed that the stepper motor had finally completely gone and
>replaced it this evening. Things seemed a little better but still, the
>idle was a bit rough and it seemed a but underpowered when under
>strain going up a steep hill. Then, after a half an hour, the check
>engine light came back on and, like clockwork the engine was running
>perfectly and able to take the steepest of hills with aplume.
>
>Sooooooooo....Now I'm guessing that BOTH the stepper motor and a
>sensor like the O2 sensor were bad. Replacing the stepper motor DID
>improve things. However, when the check engine light it coming on, it
>seems that the system is ignoring some bad input somewhere and that
>makes me suspect a sensor.
>
>Am I on the right track? Does this make any sense at all? Any ideas
>will be appreciated. This Rover is a stalwart beast that has given
>me very little trouble in the past and my heart tells me that it is
>something minor - please, let it be so!
>
>Thanks,
>
>Arden
>1993 Range Rover County LWB (Vogue LSE)
>

In news:[email protected],
Arden <[email protected]> blithered:
> Success!
>
> Thanks for all the (ahem) help.
>
> The new stepper motor did improve things as noted. However, what
> REALLY did the trick was cleaning all the contacts for the airflow
> meter, the coolant temperature sensor and the throttle position sensor
> with an old toothbrush and applying dielectric grease.
>
> Did that... and it all was as smooth as silk and the "Check Engine"
> (EFI) light has stayed off.
>
> Woo Hoo!
>
> Arden
> 1993 Range Rover County LWB (Vogue LSE)
>
>
>
> On Tue, 01 Nov 2005 17:43:04 -0800, Arden <[email protected]> wrote:
>

dielectric grease?
What's that please, sounds awfully good and I want some.

--
"He who says it cannot be done should not interrupt her doing it."

If at first you don't succeed,
maybe skydiving's not for you!

On Thu, 3 Nov 2005 11:38:35 -0000, "GbH" <[email protected]>
wrote:
>dielectric grease?
>What's that please, sounds awfully good and I want some.

It's a special grease that enhances electrical conductivity as well as
protects from corrosion. They had it in little packets at the
checkout stand of my local auto parts store the same way one might
find candy or magazines at the grocers.

Arden
1993 Range Rove County LWB (Vogue LSE)

In news:[email protected],
Arden <[email protected]> blithered:
> On Thu, 3 Nov 2005 11:38:35 -0000, "GbH" <[email protected]>
> wrote:
>> dielectric grease?
>> What's that please, sounds awfully good and I want some.
>
> It's a special grease that enhances electrical conductivity as well as
> protects from corrosion. They had it in little packets at the
> checkout stand of my local auto parts store the same way one might
> find candy or magazines at the grocers.
>
> Arden
> 1993 Range Rove County LWB (Vogue LSE)

Will have to track that down, not familiar with it over here (UK) Use Vaselin
(Petroleum Jelly) for battery terminals, otherwise contact cleaner but that is
very thin and highly volatile, probably carcinogenic too.

--
"He who says it cannot be done should not interrupt her doing it."

If at first you don't succeed,
maybe skydiving's not for you!

Arden wrote:
> On Thu, 3 Nov 2005 11:38:35 -0000, "GbH" <[email protected]>
> wrote:
>
>>dielectric grease?
>>What's that please, sounds awfully good and I want some.
>
>
> It's a special grease that enhances electrical conductivity as well as
> protects from corrosion. They had it in little packets at the
> checkout stand of my local auto parts store the same way one might
> find candy or magazines at the grocers.
>
> Arden
> 1993 Range Rove County LWB (Vogue LSE)

Dielectrics are insulators!

Dougal wrote:
> Dielectrics are insulators!

OK Perhaps but one uses them on electrical connections. Seems like you
wouldn't want an insulator there but you are right about the word
"dielectric." In any case, they definitely work.

Here is a commercial example:

http://www.midwayautosupply.com/detailedproductdescription.asp?9311