New bug, fast idle.

My 1992 Miata has started idling around 1800 rpm several days ago. It
began happening very intermittently but it's almost all the time now.

Miata.net isn't very helpful but I may not be looking in the right
place?

Today it stayed high all the time I was running errands* and it doesn't
matter if the AC is on or off but... FWIW, I left the engine running
and opened the hood to check the dashpot when I got home, it was OK but
when I wiggled the cable the idle dropped down to normal but.. the
cable was and always has been slack, maybe even a little too much slack
according to the manual so it's not the cable hanging up.... also,
manually trying to move the cable pulley has had no effect so I'm sort
of thinking it's something in the ECU telling it to idle fast?

I'd really appreciate it if someone will tell me it's either a simple
adjustment or a $1.98 part.... but I don't think so. <sigh>




*Running errand in 109F sunshine! I think just 5 more degrees and I'm
gonna put the top up and turn on the AC.

XS11E wrote:

>My 1992 Miata has started idling around 1800 rpm several days ago. It
>began happening very intermittently but it's almost all the time now.
>
>Miata.net isn't very helpful but I may not be looking in the right
>place?
>
>Today it stayed high all the time I was running errands* and it doesn't
>matter if the AC is on or off but... FWIW, I left the engine running
>and opened the hood to check the dashpot when I got home, it was OK but
>when I wiggled the cable the idle dropped down to normal but.. the
>cable was and always has been slack, maybe even a little too much slack
>according to the manual so it's not the cable hanging up.... also,
>manually trying to move the cable pulley has had no effect so I'm sort
>of thinking it's something in the ECU telling it to idle fast?
>
>I'd really appreciate it if someone will tell me it's either a simple
>adjustment or a $1.98 part.... but I don't think so. <sigh>
>
>
>*Running errand in 109F sunshine! I think just 5 more degrees and I'm
>gonna put the top up and turn on the AC.
>
>
>

For what it's worth:

Similar symptoms in my '92; turned out to be a faulty/shot "thermistor."
(The thing is located near the firewall, I think on the block.) It
sensed the engine water temperature to be cold, when in fact it was
normal running temp. The ECU, thinking "cold engine," upped the idle to
1800 rpm, just as yours.

Although I don't remember, the part was quite a bit more than $1.98.

Let us know what you find out.


'92 B; red, of course

Stuff > wrote in
:

> XS11E wrote:
>
>>My 1992 Miata has started idling around 1800 rpm several days ago.
>> It began happening very intermittently but it's almost all the
>>time now.

> For what it's worth:
>
> Similar symptoms in my '92; turned out to be a faulty/shot
> "thermistor." (The thing is located near the firewall, I think on
> the block.) It sensed the engine water temperature to be cold,
> when in fact it was normal running temp. The ECU, thinking "cold
> engine," upped the idle to 1800 rpm, just as yours.
>
> Although I don't remember, the part was quite a bit more than
> $1.98.

Darn, I was afraid of that! I don't think that would cause an
intermittent failure though?

> Let us know what you find out.

I will, I'll probably have to take it in and sell a couple of the
children to pay the bill....

XS11E wrote:
> My 1992 Miata has started idling around 1800 rpm several days ago. It
> began happening very intermittently but it's almost all the time now.
>
> Miata.net isn't very helpful but I may not be looking in the right
> place?
>
> Today it stayed high all the time I was running errands* and it doesn't
> matter if the AC is on or off but... FWIW, I left the engine running
> and opened the hood to check the dashpot when I got home, it was OK but
> when I wiggled the cable the idle dropped down to normal but.. the
> cable was and always has been slack, maybe even a little too much slack
> according to the manual so it's not the cable hanging up.... also,
> manually trying to move the cable pulley has had no effect so I'm sort
> of thinking it's something in the ECU telling it to idle fast?
>
> I'd really appreciate it if someone will tell me it's either a simple
> adjustment or a $1.98 part.... but I don't think so. <sigh>
>
>
>
>
> *Running errand in 109F sunshine! I think just 5 more degrees and I'm
> gonna put the top up and turn on the AC.

XS11E,

I have a few suggestions...they may not be right, but they're free/very
cheap to check.

1) Check to make sure the cable pulley is well lubricated along both
the point-of-contact with the cable and where it connects to the
throttle body. On the cable I'd recommend lithium grease, but others
might say otherwise for the actual joint.

2) Remove the intake piping from the throttle body. Say hello to your
butterfly valve. With your (clean) finger, poke at it (on the bottom
half, I believe) and see how easily it moves. Keep an eye out for any
obstructing debris in there. Lubricate where the butterfly valve joins
to the throttle body.

3) This may be a case of a loose idle valve somewhere. Notice how when
the car is cold, it idles at a different speed? There's usually two
idling lines that allow specified amounts of air in. I'm not sure how
this works on a Miata, but it's something to look into.

4) Gas pedal sticking?

Also, some things to ponder: does it only happen when it's that
absurdly hot out? Does the idle jump even higher when you turn on the
AC/radio/12V microwave oven?

Keep fiddling!

-r0ll

r0lliSl1fe wrote:

> I have a few suggestions...they may not be right, but they're free/very
> cheap to check.

Thanks, I appreciate them!

> 1) Check to make sure the cable pulley is well lubricated along both
> the point-of-contact with the cable and where it connects to the
> throttle body. On the cable I'd recommend lithium grease, but others
> might say otherwise for the actual joint.

I'll check that. Hadn't thought of doing that.

> 2) Remove the intake piping from the throttle body. Say hello to your
> butterfly valve. With your (clean) finger, poke at it (on the bottom
> half, I believe) and see how easily it moves. Keep an eye out for any
> obstructing debris in there. Lubricate where the butterfly valve joins
> to the throttle body.

I don't think it could be anything in there causing the butterfly to
stick because I've tried closing it from the outside and it seems to be
closed tightly but I'll take a look and see what I can find from the
inside.

> 4) Gas pedal sticking?

No, the cable is slack when the car is idling fast so I've eliminated
that, along with the cruise control cable, etc. The problem has to be
right at the throttle body but from checking so far I'm pretty sure
it's the ECU telling it to idle fast, not the butterfly failing to
close.

> Also, some things to ponder: does it only happen when it's that
> absurdly hot out?

I don't know, we've only got a cool nice comfortable 110F and won't get
down to the too-cold-to-support-human-life temperatures of 85F and
below for several more months...

> Does the idle jump even higher when you turn on the
> AC/radio/12V microwave oven?

Here's something a bit weird. Before the problem, when I'd turn on the
AC the idle would start to drop and almost immediately go back to a
normal 1,000 rpm. Now, when it's idling up at 1,800 turning on the AC
acts the same, the idle speed just barely starts drop and then
immediately goes back to 1,800. It's as if the ECU is saying the
correct idle speed is 1,800rpm and is keeping it at that speed AND
that's why I don't suspect any mechanical problem but... I'll keep
checking as that's all I can do.

Oh, FWIW, I've not had a "check engine" light at all, whatever's
happening the computer thinks is normal.

wrote in
ups.com:

OK, the fast idle problem is fixed. Anyone want to make a guess as to
the problem? The first one to post with the correct solution to the
problem will win a one year free subscription to Nigerian scam emails!
<g>

In article >,
XS11E > wrote:

> OK, the fast idle problem is fixed. Anyone want to make a guess as to
> the problem?

The wire fell off the temperature sensor.

--
Lanny Chambers
'94C, St. Louis
http://www.hummingbirds.net/alignment.html

Lanny Chambers > wrote in
:

> In article >,
> XS11E > wrote:
>
>> OK, the fast idle problem is fixed. Anyone want to make a guess
>> as to the problem?
>
> The wire fell off the temperature sensor.

Not even close!

In article >,
XS11E > wrote:

> >> OK, the fast idle problem is fixed. Anyone want to make a guess
> >> as to the problem?
> >
> > The wire fell off the temperature sensor.
>
> Not even close!

Um...the tach was wrong, and it wasn't actually idling too fast?

Crikey, how should we know? :-)

--
Lanny Chambers
'94C, St. Louis
http://www.hummingbirds.net/alignment.html

Lanny Chambers > wrote in
:

> In article >,
> XS11E > wrote:
>
>> >> OK, the fast idle problem is fixed. Anyone want to make a
>> >> guess as to the problem?
>> >
>> > The wire fell off the temperature sensor.
>>
>> Not even close!
>
> Um...the tach was wrong, and it wasn't actually idling too fast?
>
> Crikey, how should we know? :-)

I wish one of you had told me, apparently it's not a rare problem. I
took it to Mike's Place:

http://www.mikes-place.biz/

After talking to Mike on the phone, he just asked the year and then
said it might be the IAC but most likely was the PVC valve and he could
look at it at 2pm.

The PVC valve had lost it's innards and was just an empty shell. The
extra air caused the ECU to add fuel and the car ran just like I was
stepping on the gas. Since the problem was entirely mechanical, no
Check Engine Light.

Mike had a PCV valve for $5.00 and I was off and running (with proper
idle speed) about 20 minutes after I brought the car in....

As I've said hundreds of times before, it's hard to diagnose a problem
as fast as someone who's seen it before!