Bad idle on '91 626

Here is the problem.

'91 Mazda 626 2.2 without turbo (Yeah, I wish.) has a rolling miss at
idle when in gear. It runs and idles smoothly at all other times, but
if the car is fully warmed up and I stop at a traffic light, it will
idle smoothly for about four or five seconds, then the idle will drop
and surge, drop and surge, from almost stalled to normal. If I put it
back into gear it will go right to normal (750 rpm) and stay there.

I have looked for a vacuum leak, but there could still be one that I
missed. (Zillions of hoses.) I know that it could be just about
anything, but I wonder whether there's anything that jumps to mind as
a likley suspect. The manual talks about troubleshooting the various
controls using an "SST." Unless they mean the Concorde, I don't know
what that is. Do I need to corner the Snap-on man? How much will he
do me for?

I realize that if you don't have all the diagnostic stuff, sometimes
the only available approach is to replace something to find out
whether that is the problem, but I don't really know where to start.
If you say, "Try replacing the throttle sensor." and I do and it
doesn't straighten it out, I am not going to be miffed. I just don't
have a best guess.

Thanks for any help you can offer.

Hamish

A 'searching idle' is commonly cured by a slight fuel/air idle mixture
adjustment.
Not familiar with this model as to adjustment screw or components that
affect this.
rick

"Hamish WAUGH" > wrote in message
...
> Here is the problem.
>
> '91 Mazda 626 2.2 without turbo (Yeah, I wish.) has a rolling miss at
> idle when in gear. It runs and idles smoothly at all other times, but
> if the car is fully warmed up and I stop at a traffic light, it will
> idle smoothly for about four or five seconds, then the idle will drop
> and surge, drop and surge, from almost stalled to normal. If I put it
> back into gear it will go right to normal (750 rpm) and stay there.
>
> I have looked for a vacuum leak, but there could still be one that I
> missed. (Zillions of hoses.) I know that it could be just about
> anything, but I wonder whether there's anything that jumps to mind as
> a likley suspect. The manual talks about troubleshooting the various
> controls using an "SST." Unless they mean the Concorde, I don't know
> what that is. Do I need to corner the Snap-on man? How much will he
> do me for?
>
> I realize that if you don't have all the diagnostic stuff, sometimes
> the only available approach is to replace something to find out
> whether that is the problem, but I don't really know where to start.
> If you say, "Try replacing the throttle sensor." and I do and it
> doesn't straighten it out, I am not going to be miffed. I just don't
> have a best guess.
>
> Thanks for any help you can offer.
>
> Hamish

On Sun, 30 Jan 2005 11:46:15 -0500, Hamish WAUGH > wrote:
>Here is the problem.

>'91 Mazda 626 2.2 without turbo (Yeah, I wish.) has a rolling miss at
>idle when in gear. It runs and idles smoothly at all other times, but
>if the car is fully warmed up and I stop at a traffic light, it will
>idle smoothly for about four or five seconds, then the idle will drop
>and surge, drop and surge, from almost stalled to normal. If I put it
>back into gear it will go right to normal (750 rpm) and stay there.

>I have looked for a vacuum leak, but there could still be one that I
>missed. (Zillions of hoses.) I know that it could be just about

There should NOT be zillions of vacuum lines unless somehow mazda slipped
you an engine from the late 70's.

There should be less than a half dozen actuall vacuum lines. Stuff like the
brake power unit, the idle air manifold, and the cruise control actuator.
Start at the intake manifold and look for stuff coming off it.

Does the ECU report any errors? Is your ignition system perfect -- nice fat
spark if you pull a wire and hold it 1/4-1/3" from a ground? Timing correct?

Don't replace anything unless you've actually tested it bad. One mistake will
easily cost you more than having a mechanic diagnose the problem.

Hamish WAUGH wrote:
> Here is the problem.
>
> '91 Mazda 626 2.2 without turbo (Yeah, I wish.) has a rolling miss at
> idle when in gear. It runs and idles smoothly at all other times, but
> if the car is fully warmed up and I stop at a traffic light, it will
> idle smoothly for about four or five seconds, then the idle will drop
> and surge, drop and surge, from almost stalled to normal. If I put it
> back into gear it will go right to normal (750 rpm) and stay there.
>
> I have looked for a vacuum leak, but there could still be one that I
> missed. (Zillions of hoses.) I know that it could be just about
> anything, but I wonder whether there's anything that jumps to mind as
> a likley suspect. The manual talks about troubleshooting the various
> controls using an "SST." Unless they mean the Concorde, I don't know
> what that is. Do I need to corner the Snap-on man? How much will he
> do me for?
>
> I realize that if you don't have all the diagnostic stuff, sometimes
> the only available approach is to replace something to find out
> whether that is the problem, but I don't really know where to start.
> If you say, "Try replacing the throttle sensor." and I do and it
> doesn't straighten it out, I am not going to be miffed. I just don't
> have a best guess.
>
> Thanks for any help you can offer.
>
> Hamish

I very common failure with these (I own a 91 626 and I'm also a
mechanic), is small cracks in the intake air hose. These are very hard
to see without removing the hose. I fixed mine by wrapping the entire
hose with 2 layers of electrical tape.

Larry

On Sun, 30 Jan 2005 14:06:23 -0600, TCS
> wrote:

>There should NOT be zillions of vacuum lines unless somehow mazda slipped
>you an engine from the late 70's.
>
>There should be less than a half dozen actuall vacuum lines. Stuff like the
>brake power unit, the idle air manifold, and the cruise control actuator.
>Start at the intake manifold and look for stuff coming off it.

================
Well, I'm kind of an old-timer. More than one going to the
distributor (and in the really old days, one going to the wipers) kind
of throws me.
================

>Does the ECU report any errors?

================
No errors show on the dash, but I don't think it is equipped to do
that. Doesn't seem to have a "Check Engine" light or whatever.

Is there a port to plug into with a relatively affordable unit to read
out such codes? I could use a hint like that.
===============


Is your ignition system perfect -- nice fat
>spark if you pull a wire and hold it 1/4-1/3" from a ground? Timing correct?


==============
Timing is dead-on. Plugs are new within three months. Cap and rotor
new. Wires could be questionable. Filters are good. Haven't checked
spark, but will on Saturday, if the weather is bearable.
=============

>
>Don't replace anything unless you've actually tested it bad. One mistake will
>easily cost you more than having a mechanic diagnose the problem.

============
I only meant that, if this is a textbook case of the symptoms of some
particular failed control, part that I would be willing to roll the
dice. No, I don't want to go replacing bushels of parts on a whim.

PLEASE NOTE that the idle only goes silly when the car is in DRIVE.
Not Park, not neutral, and not even when it is in REVERSE. This seems
kind of odd to me.

Thanks for any help you can offer,

Hamish

Original Post Below:

>On Sun, 30 Jan 2005 11:46:15 -0500, Hamish WAUGH > wrote:
>>Here is the problem.
>
>>'91 Mazda 626 2.2 without turbo (Yeah, I wish.) has a rolling miss at
>>idle when in gear. It runs and idles smoothly at all other times, but
>>if the car is fully warmed up and I stop at a traffic light, it will
>>idle smoothly for about four or five seconds, then the idle will drop
>>and surge, drop and surge, from almost stalled to normal. If I put it
>>back into gear it will go right to normal (750 rpm) and stay there.
>
>>I have looked for a vacuum leak, but there could still be one that I
>>missed. (Zillions of hoses.) I know that it could be just about

On Tue, 01 Feb 2005 08:43:40 -0500, Hamish WAUGH > wrote:
>On Sun, 30 Jan 2005 14:06:23 -0600, TCS
> wrote:

>>There should NOT be zillions of vacuum lines unless somehow mazda slipped
>>you an engine from the late 70's.
>>
>>There should be less than a half dozen actuall vacuum lines. Stuff like the
>>brake power unit, the idle air manifold, and the cruise control actuator.
>>Start at the intake manifold and look for stuff coming off it.

>================
>Well, I'm kind of an old-timer. More than one going to the
>distributor (and in the really old days, one going to the wipers) kind
>of throws me.
>================
There shouldn't be any going to the distributor. All that's done in the
ECU nowadays. Did a '91 vehicle really have a vacuum advance? I'd be
amazed if that was really true.



>>Does the ECU report any errors?

>================
>No errors show on the dash, but I don't think it is equipped to do
>that. Doesn't seem to have a "Check Engine" light or whatever.
An ECU will often have errors to report without lighting the check-engine
light. There's usually a procedure like flipping a switch and then turning
the ignition on, or doing something wierd like turning the ignition on
then off 3 times within 10 seconds.




>Is there a port to plug into with a relatively affordable unit to read
>out such codes? I could use a hint like that.
>===============
Many car parts stores will read the codes to you for free as it is good for
their business to do so. Autozone for example.

....

In article >,
says...
> Hamish WAUGH wrote:
> > Here is the problem.
> >
> > '91 Mazda 626 2.2 without turbo (Yeah, I wish.) has a rolling miss at
> > idle when in gear. It runs and idles smoothly at all other times, but
> > if the car is fully warmed up and I stop at a traffic light, it will
> > idle smoothly for about four or five seconds, then the idle will drop
> > and surge, drop and surge, from almost stalled to normal. If I put it
> > back into gear it will go right to normal (750 rpm) and stay there.
> >
> > I have looked for a vacuum leak, but there could still be one that I
> > missed. (Zillions of hoses.) I know that it could be just about
> > anything, but I wonder whether there's anything that jumps to mind as
> > a likley suspect. The manual talks about troubleshooting the various
> > controls using an "SST." Unless they mean the Concorde, I don't know
> > what that is. Do I need to corner the Snap-on man? How much will he
> > do me for?
> >
> > I realize that if you don't have all the diagnostic stuff, sometimes
> > the only available approach is to replace something to find out
> > whether that is the problem, but I don't really know where to start.
> > If you say, "Try replacing the throttle sensor." and I do and it
> > doesn't straighten it out, I am not going to be miffed. I just don't
> > have a best guess.
> >
> > Thanks for any help you can offer.
> >
> > Hamish
>
> I very common failure with these (I own a 91 626 and I'm also a
> mechanic), is small cracks in the intake air hose. These are very hard
> to see without removing the hose. I fixed mine by wrapping the entire
> hose with 2 layers of electrical tape.
>
> Larry
>
I did mine with duct tape. Take the intake "boot" off and inspect by
flexing it. Cracks do not appear in the "valleys" but do on the "peaks"
on mine.

Al