Idle problem

humed · Post by **humed** » Mon Jun 12, 2000 1:27 pm

I've got a problem with my 91. It is occasionally stalling when I am
decelerating to come to a stop.
It only happens when the engine is at normal operating temparature and
seems to occur more when I have been running at open road speeds for a
period of time.

The leads and spark plugs have recently been replaced so I'm ruling these
out. Could the problem have something to do with the idle speed control
valve or should I be looking elsewhere?

Thanks

Dave

RAY · Post by **RAY** » Mon Jun 12, 2000 2:00 pm

Dave
The first thing you have to establish has it just started to
happen...first check your air filter then your timing as you
have changed your leads and plugs ( i have known new plugs to be gapped
wrong should be around 1mm)...only then adjust your idle speed it
should be around 900 rpm ...if you do change your idle speed make a
note of where it was ( turn the idle screw out a quarter of a turn at a
time) so if nothing changes after the checks you can put it back as the
problem may be else wear...ie fuel filter, or you may have an air
leak

--

Regards
Ray

RAY · Post by **RAY** » Mon Jun 12, 2000 2:00 pm

Dave
The first thing you have to establish has it just started to
happen...first check your air filter then your timing as you
have changed your leads and plugs ( i have known new plugs to be gapped
wrong should be around 1mm)...only then adjust your idle speed it
should be around 900 rpm ...if you do change your idle speed make a
note of where it was ( turn the idle screw out a quarter of a turn at a
time) so if nothing changes after the checks you can put it back as the
problem may be else wear...ie fuel filter, or you may have an air
leak

--

Regards
Ray

humed · Post by **humed** » Mon Jun 12, 2000 4:07 pm

Ray,

My car has a new air filter, plugs are all gapped correctly, and idle is
900rpm. I also thought about the fuel filter as a possibility but if it
was blocked wouldn't my car be having problems like holding it's speed when
I accelerate?

You mention air leaks - How do I look for these?

Thanks

Dave

RAY
<ray.yp.smith@x To: mx5list@mx5club.org.nz
tra.co.nz> cc:
Sent by: Subject: Re: Idle problem
listadmin@mx5cl
ub.org.nz

12/06/2000
13:58
Please respond
to mx5list

Dave
The first thing you have to establish has it just started to
happen...first check your air filter then your timing as you
have changed your leads and plugs ( i have known new plugs to be gapped
wrong should be around 1mm)...only then adjust your idle speed it
should be around 900 rpm ...if you do change your idle speed make a
note of where it was ( turn the idle screw out a quarter of a turn at a
time) so if nothing changes after the checks you can put it back as the
problem may be else wear...ie fuel filter, or you may have an air
leak

--

Regards
Ray

RAY · Post by **RAY** » Mon Jun 12, 2000 5:07 pm

Dave
You are correct with the fuel filter, you would have power problems, i take it
you have none of these, as regard to air leaks you can usually hear them, have
you checked the timing, another thing i've seen before is no free play in the
accelerator cable, its very difficult to diagnose without seeing your car as
you have covered all of the normal checks, has the problem just started?
if you are in the Auckland area i will be available to have a look tomorrow
during the day if you like
Ray

humed@farmers.co.nz wrote:

[...]

should be around 900 rpm ...if you do change your idle speed make a
note of where it was ( turn the idle screw out a quarter of a turn at a
time) so if nothing changes after the checks you can put it back as the
problem may be else wear...ie fuel filter, or you may have an air
leak

--

Regards
Ray

--

Regards
Ray

RAY · Post by **RAY** » Mon Jun 12, 2000 5:07 pm

Dave
You are correct with the fuel filter, you would have power problems, i take it
you have none of these, as regard to air leaks you can usually hear them, have
you checked the timing, another thing i've seen before is no free play in the
accelerator cable, its very difficult to diagnose without seeing your car as
you have covered all of the normal checks, has the problem just started?
if you are in the Auckland area i will be available to have a look tomorrow
during the day if you like
Ray

humed@farmers.co.nz wrote:

[...]

should be around 900 rpm ...if you do change your idle speed make a
note of where it was ( turn the idle screw out a quarter of a turn at a
time) so if nothing changes after the checks you can put it back as the
problem may be else wear...ie fuel filter, or you may have an air
leak

--

Regards
Ray

--

Regards
Ray

Debra · Post by **Debra** » Mon Jun 12, 2000 5:39 pm

My '90 has the exact same problem. When I took my car in for its service it did not do it to show the mechanic the problem and he had checked everything else out. If you find the problem please share as it can be quite embarassing stalling as you cruise up to the lights!

Thanks

Debra
--

On Mon, 12 Jun 2000 17:07:02 RAY wrote:
[...]

Regards
Ray
--

Regards
Ray

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Edwin de Beun · Post by **Edwin de Beun** » Mon Jun 12, 2000 8:19 pm

Hi Dave, Debra, Ray and fellow MX5 club members.

Our '91 does the same. My mechanic has no idea why either. Everything
seems to check OK. The problem is not there all the time, however I have
been decelerating with the clutch disengaged to prevent stalling. Not my
preferred method, but stalling the engine regularly is quite embarrassing.

The problem has been there for the last few months, but I have been unable
to find a solution.

Any ideas would be great. Thanks very much,

Edwin

RAY · Post by **RAY** » Tue Jun 13, 2000 8:26 am

This is a common problem on older MX5's and it is usually caused by the battery,
if anybody is still running with the original battery then it is recommended
that you change it, 4-5yrs is the normal time to replace it, or indeed if your
battery shows signs of deteriorating then change it as it causes problems with
your ECU that monitors your electric's which in turn monitors your engine, also
make sure your damper on the throttle return is working, this stops the throttle
returning with a bang onto the throttle stop, another problem with older MX5's
is wear on the throttle stop, the stop is hidden under the throttle body and is
a grub screw with a locknut on it, you can turn this in a quarter of a turn then
slow your idle screw in to adjust the idle speed back to 900 rpm this is a last
resort cure and has worked for me and other members, Edwin's cure is a what a
lot of people do but is frustrating to say the least but can be cured

Ray

Edwin de Beun wrote:

[...]

humed · Post by **humed** » Tue Jun 13, 2000 10:00 am

Hi Ray,

Re your comments about the battery, If the battery is the problem why does
the problem not happen everytime I am
decelerating?

Thanks

Dave

RAY
<ray.yp.smith@x To: mx5list@mx5club.org.nz
tra.co.nz> cc:
Sent by: Subject: Re: Idle problem
listadmin@mx5cl
ub.org.nz

13/06/2000
08:22
Please respond
to mx5list

This is a common problem on older MX5's and it is usually caused by the
battery,
if anybody is still running with the original battery then it is
recommended
that you change it, 4-5yrs is the normal time to replace it, or indeed if
your
battery shows signs of deteriorating then change it as it causes problems
with
your ECU that monitors your electric's which in turn monitors your engine,
also
make sure your damper on the throttle return is working, this stops the
throttle
returning with a bang onto the throttle stop, another problem with older
MX5's
is wear on the throttle stop, the stop is hidden under the throttle body
and is
a grub screw with a locknut on it, you can turn this in a quarter of a turn
then
slow your idle screw in to adjust the idle speed back to 900 rpm this is a
last
resort cure and has worked for me and other members, Edwin's cure is a what
a
lot of people do but is frustrating to say the least but can be cured

Ray

Edwin de Beun wrote:

Hi Dave, Debra, Ray and fellow MX5 club members.

Our '91 does the same. My mechanic has no idea why either. Everything
seems to check OK. The problem is not there all the time, however I have
been decelerating with the clutch disengaged to prevent stalling. Not my
preferred method, but stalling the engine regularly is quite

embarrassing.

The problem has been there for the last few months, but I have been

unable
[...]

RAY · Post by **RAY** » Tue Jun 13, 2000 10:41 am

Dave
Not being an electronics expert i'm not sure, i'm told a voltage drop changes
the ECU readings or confuses it, so giving different readings and measurements
analyzing throttle position, mixture,etc,etc...hence can lead to idle
problems, and in some cases a performance problem, there is a throttle position
sensor on the throttle body, all i know is one MX5 i had with an original
battery was changed for a new one and the idle was then 1500 rpm...had me
scratching my head on that one, you could try swapping a battery with someone
just to see if it eliminates it, it is a known fact that you need a good
battery to run electronics

humed@farmers.co.nz wrote:

[...]

RAY · Post by **RAY** » Tue Jun 13, 2000 10:41 am

Dave
Not being an electronics expert i'm not sure, i'm told a voltage drop changes
the ECU readings or confuses it, so giving different readings and measurements
analyzing throttle position, mixture,etc,etc...hence can lead to idle
problems, and in some cases a performance problem, there is a throttle position
sensor on the throttle body, all i know is one MX5 i had with an original
battery was changed for a new one and the idle was then 1500 rpm...had me
scratching my head on that one, you could try swapping a battery with someone
just to see if it eliminates it, it is a known fact that you need a good
battery to run electronics

humed@farmers.co.nz wrote:

[...]

humed · Post by **humed** » Tue Jun 13, 2000 10:41 am

Ray,

Thanks for all the advice. I'll give the battery swap a go to see if it
makes a difference.

Dave

RAY
<ray.yp.smith@x To: mx5list@mx5club.org.nz
tra.co.nz> cc:
Sent by: Subject: Re: Idle problem
listadmin@mx5cl
ub.org.nz

13/06/2000
10:36
Please respond
to mx5list

Dave
Not being an electronics expert i'm not sure, i'm told a voltage drop
changes
the ECU readings or confuses it, so giving different readings and
measurements
analyzing throttle position, mixture,etc,etc...hence can lead to idle
problems, and in some cases a performance problem, there is a throttle
position
sensor on the throttle body, all i know is one MX5 i had with an original
battery was changed for a new one and the idle was then 1500 rpm...had me
scratching my head on that one, you could try swapping a battery with
someone
just to see if it eliminates it, it is a known fact that you need a good
battery to run electronics

humed@farmers.co.nz wrote:

Hi Ray,

Re your comments about the battery, If the battery is the problem why

does
[...]

This is a common problem on older MX5's and it is usually caused by the
battery,
if anybody is still running with the original battery then it is
recommended
that you change it, 4-5yrs is the normal time to replace it, or indeed if
your
battery shows signs of deteriorating then change it as it causes problems
with
your ECU that monitors your electric's which in turn monitors your

engine,

also
make sure your damper on the throttle return is working, this stops the
throttle
returning with a bang onto the throttle stop, another problem with older
MX5's
is wear on the throttle stop, the stop is hidden under the throttle body
and is
a grub screw with a locknut on it, you can turn this in a quarter of a

turn

then
slow your idle screw in to adjust the idle speed back to 900 rpm this is

a

last
resort cure and has worked for me and other members, Edwin's cure is a

what

a
lot of people do but is frustrating to say the least but can be cured

Ray

Edwin de Beun wrote:

Hi Dave, Debra, Ray and fellow MX5 club members.

Our '91 does the same. My mechanic has no idea why either. Everything
seems to check OK. The problem is not there all the time, however I

have

been decelerating with the clutch disengaged to prevent stalling. Not

my
[...]

Post by **zorruno** » Tue Jun 13, 2000 11:03 am

I've heard this comment before about batteries, but I am a bit skeptical. My
battery is still original (in so far as I can can tell, having looked at all
tell tail signs) and it is a 94. I would expect an Glass Matt type battery
to last 6-8 years or more if looked after properly. (That's if you still
have this type of battery installed)

I don't have an in depth knowledge of the mx5 ecu, but, I wouldn't have
thought that a battery - even dropping to about 10.5 volts (which is what I
would guess a 99% discharged battery would measure without load, and
obviously without the alternator running) would prevent the ECU from doing
its stuff. The ECU would have some sort of DC to DC converter or regulator
to keep the processor running probably down to less than 9 volts.

In saying that, however - before buying a new battery - you could try
disconnecting it and give it a 1 to 2 Amp charge overnight and see if the
problem goes away for the next few days. You can also sometimes completely
cure a problematic AGM battery by doing this.

Now if the altenator wasn't functioning properly, or there was a ground
connection problem somewhere, this may give intermittant ecu problems. A
new battery may cover up an alternator problem for a while - I found this
out on a previous car.

I'd try the mechanical fixes first - but being only a mechanic novice (first
oil change ever 12 months ago!)
I'm always quick to blame the mechanical aspects first...

YMMV
Cheers
H.

RAY · Post by **RAY** » Tue Jun 13, 2000 11:36 am

Howard
You could be right on the voltage drop, the battery i changed did drop
to 11 volts that's why i changed it, you could be right on the ground
side i've come across bad connections at the battery on many occasions,
so your comments on alternator problems are very valid, i guess that's
where a good auto electrician could be handy.
while i think of it, mainly for new members, it is common knowledge to
most members that the 1800 has two parameters...one economy and one
performance, if you disconnect the battery over night then reconnect it
go for a hard drive round the block the ECU resets itself to the
performance mode, so if anybody has disconnected their battery at any
time and they are wondering why the performance has changed it probably
reset itself to the economy mode, this does not work for the 1600 if any
body is wondering.

--

Regards
Ray

RAY · Post by **RAY** » Tue Jun 13, 2000 11:36 am

Howard
You could be right on the voltage drop, the battery i changed did drop
to 11 volts that's why i changed it, you could be right on the ground
side i've come across bad connections at the battery on many occasions,
so your comments on alternator problems are very valid, i guess that's
where a good auto electrician could be handy.
while i think of it, mainly for new members, it is common knowledge to
most members that the 1800 has two parameters...one economy and one
performance, if you disconnect the battery over night then reconnect it
go for a hard drive round the block the ECU resets itself to the
performance mode, so if anybody has disconnected their battery at any
time and they are wondering why the performance has changed it probably
reset itself to the economy mode, this does not work for the 1600 if any
body is wondering.

--

Regards
Ray

Post by **zorruno** » Tue Jun 13, 2000 11:52 am

Or, Carly/Howard mode...

H & J Weir · Post by **H & J Weir** » Tue Jun 13, 2000 8:27 pm

How do Ray.
It's been interesting to follow the discussion on occasional stalling - I
have also been blessed with this. What interested me was your idea on a weak
battery as a possible cause, because since I had a new battery fitted, I
haven't had a recurrence of the problem. I reckon you've cracked it.
Keep up the good work.
Cheers
Howard Weir.
Dunedin.

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