What causes idle speed to be low?

[Ken Blake]

I have a Mitsubishi Lancer 2003 which has low idle speed.
So low that it stalls unless I keep the gas on the peddle.

What causes that?
And more important, how can I adjust it?

Where do I get more information specific to the vehicle?

[micky]

In alt.home.repair, on Mon, 16 Sep 2024 20:52:55 -0600, Ken Blake

Post by Ken Blake
I have a Mitsubishi Lancer 2003 which has low idle speed.
So low that it stalls unless I keep the gas on the peddle.
What causes that?
And more important, how can I adjust it?
Where do I get more information specific to the vehicle?

Have you checked the engine codes yet? Buy a code reader or go to a
place like AutoZone where they will read them for you for free. They
have a wealth of information. Get both the active codes and the pending
codes.

They didn't have this style when I bought mine, but it seems like it
would be economical,

https://www.amazon.com/Bluetooth-OBD2-Scanner-APP-Car/dp/B0D3L7TGGL/ref=sr_1_3_sspa
https://www.amazon.com/Dickno-Car-Auto-Diagnostic-Scanner/dp/B0CMWVBZFS/ref=sr_1_19

The first is $30 and the second is 6. I'm going to guess that the first
one is better, but I haven't read the page yet.

Both of them schould work with just about every car sold for the last
few years, and the expensive one will probably be updated for future
cars for several more years.

These don't do transmission codes afaik. Well one comment says the
expensive one does "OBD scanners plug into your car’s OBD-II port to
read and clear diagnostic trouble codes (DTCs), identifying issues like
engine misfires and transmission problems.". Iow, it includes
transmissions but the comment is from a girl and what do they know? No,
I'd doubt it no matter who said it.

I'll have to read this later.
https://www.jbtools.com/blog/how-to-read-your-cars-transmission-codes/
But anyhow, your transmission is not the problem, of course. I brought
that up.

Plus there are the standard, original style with a built in screen and
button contols.

[micky]

In alt.home.repair, on Mon, 16 Sep 2024 23:13:35 -0400, micky

Post by micky
In alt.home.repair, on Mon, 16 Sep 2024 20:52:55 -0600, Ken Blake

Post by Ken Blake
I have a Mitsubishi Lancer 2003 which has low idle speed.
So low that it stalls unless I keep the gas on the peddle.
What causes that?
And more important, how can I adjust it?
Where do I get more information specific to the vehicle?

Have you checked the engine codes yet? Buy a code reader or go to a
place like AutoZone where they will read them for you for free. They
have a wealth of information. Get both the active codes and the pending
codes.
They didn't have this style when I bought mine, but it seems like it
would be economical,
https://www.amazon.com/Bluetooth-OBD2-Scanner-APP-Car/dp/B0D3L7TGGL/ref=sr_1_3_sspa
https://www.amazon.com/Dickno-Car-Auto-Diagnostic-Scanner/dp/B0CMWVBZFS/ref=sr_1_19
The first is $30 and the second is 6. I'm going to guess that the first
one is better, but I haven't read the page yet.
Both of them schould work with just about every car sold for the last
few years, and the expensive one will probably be updated for future
cars for several more years.
These don't do transmission codes afaik. Well one comment says the
expensive one does "OBD scanners plug into your car’s OBD-II port to
read and clear diagnostic trouble codes (DTCs), identifying issues like
engine misfires and transmission problems.". Iow, it includes
transmissions but the comment is from a girl and what do they know? No,
I'd doubt it no matter who said it.
I'll have to read this later.
https://www.jbtools.com/blog/how-to-read-your-cars-transmission-codes/
But anyhow, your transmission is not the problem, of course. I brought
that up.
Plus there are the standard, original style with a built in screen and
button contols.

Search google for Read Transmission Codes and one hit is in Amazon
"transmission diagnostic tool" but don't assume that every hit will
actually read transmission codes. Amazon will mix in things that don't
meet the search criteria with things that do meet them!! It does this
all the time.

The ones that do read xmission codes seem pretty expensive. (Long story
about the time I had a transmission problem for a while, deleted.)
https://www.amazon.com/s?k=transmission+diagnostic+tool&hvadid=198584141511&hvdev=c&hvlocphy=9007877&hvnetw=g&hvqmt=b&hvrand=8491758172442501026&hvtargid=kwd-295643102619&hydadcr=7517_9880911&tag=googhydr-20&ref=pd_sl_6l1qjvcpb6_b


And then there are airbag codes. Cheap readers don't read them either,
but you don't have to read those. Just wait until there is a collision
and see if the bag opens. I suppose they turn on the Check engine
light, or is there a check bag light?

[Woozy Song]

Post by micky
And then there are airbag codes. Cheap readers don't read them either,
but you don't have to read those. Just wait until there is a collision
and see if the bag opens. I suppose they turn on the Check engine
light, or is there a check bag light?

Most cars I have driven had a specific telltale light for airbags,
and another telltale for ABS/ESC stuff.

[Paul in Houston TX]

Post by Ken Blake
I have a Mitsubishi Lancer 2003 which has low idle speed.
So low that it stalls unless I keep the gas on the peddle.
What causes that?
And more important, how can I adjust it?

It could be due to a bad or clogged sensor:
MAF, TPS, IAC, IAT, MAT, O2. My guess is TPS or IAC.

You can clean the MAF, IAT, and possibly the IAC.
You can check the ohms of most of them.
Most of the sensors run at 5 volts due to using TTL circuits.
You can check voltages of many of them at KOEO (key on, engine off).
The O2 should be between 0.1 and 1.0 volts depending on temp.

Post by Ken Blake
Where do I get more information specific to the vehicle?

This shows some data... don't know where to get the manual.
https://www.evolutionm.net/forums/lancer-how-requests-questions-tips/465622-intake-air-temp-sensor.html
https://www.evolutionm.net/forums/general-engine-management-tuning-forum/472030-proper-ohms-tps.html
and pictures:
https://www.ebay.com/b/Air-Intake-Fuel-Sensors-for-2003-Mitsubishi-Lancer/33557/bn_87603784

[Scott Dorsey]

Post by Ken Blake
I have a Mitsubishi Lancer 2003 which has low idle speed.
So low that it stalls unless I keep the gas on the peddle.
What causes that?

You're thinking backwards. Think about what happens when you're at idle.
Something needs to happen to make the mixture more rich, and that could be
done in all kinds of different ways. Some cars have an extra injector just
for idle, some have software in the ECU that runs the normal injectors more
rich, some have a gadget in the carb that is activated by engine vacuum.

I have never worked on a Lancer, but less than a minute with Alldata shows
me that you have an idle control valve. Check it and make sure it is
functioning properly. Is it getting a control signal from the computer
to open and close? The meter will tell you. Is it actually opening and
closing? Your finger blocking the entrance will tell you.

Plenty of other things can cause the mixture to get messed up at idle and
that includes vacuum leaks, so if the valve is operating properly checking
out the vacuum lines is your next step.

If you use a crappy scanner that just gives you codes, you will see a bunch
of codes saying the mixture is wrong, but you already know that. You don't
need the scanner to tell you.

If you use a proper mechanic's scanner you can see all the inputs coming into
the ECU, which includes the mass air flow sensor, and you can see if those
inputs are good and whether or not the ECU is opening and closing the valve
properly. This is useful information but the most important information
comes from your eyes and ears.

Post by Ken Blake
And more important, how can I adjust it?

You do not, you fix it.

Post by Ken Blake
Where do I get more information specific to the vehicle?

Alldata will get you a manual if you don't have one, but for this car
even a Haynes will probably tell you what you want.
--scott

[Snag]

Post by Scott Dorsey

Post by Ken Blake
I have a Mitsubishi Lancer 2003 which has low idle speed.
So low that it stalls unless I keep the gas on the peddle.
What causes that?

You're thinking backwards. Think about what happens when you're at idle.
Something needs to happen to make the mixture more rich, and that could be
done in all kinds of different ways. Some cars have an extra injector just
for idle, some have software in the ECU that runs the normal injectors more
rich, some have a gadget in the carb that is activated by engine vacuum.

.

Post by Scott Dorsey
--scott

A total crock of shit Scott . Idle mix is NOT enriched , if anything
it's leaned out . I strongly suspect it's either an IAC or the MAF
sensor that's malfunctioning - IAC is most likely , and can USUALLY be
cleared up with being cleaned with carb spray . The best thing for him
to do is have one of the local parts stores run an OBDC2 scan . Just
about every parts store does this for free . Makes sales for them and
saves the customer money by not just throwing parts at an undiagnosed
problem .

[Max Demian]

Post by Ken Blake
I have a Mitsubishi Lancer 2003 which has low idle speed.
So low that it stalls unless I keep the gas on the peddle.
What causes that?

You're thinking backwards.  Think about what happens when you're at idle.
Something needs to happen to make the mixture more rich, and that could be
done in all kinds of different ways.  Some cars have an extra injector
just
for idle, some have software in the ECU that runs the normal injectors more
rich, some have a gadget in the carb that is activated by engine vacuum.

  A total crock of shit Scott . Idle mix is NOT enriched , if anything
it's leaned out . I strongly suspect it's either an IAC or the MAF
sensor that's malfunctioning - IAC is most likely , and can USUALLY be
cleared up with being cleaned with carb spray . The best thing for him
to do is have one of the local parts stores run an OBDC2 scan . Just
about every parts store does this for free . Makes sales for them and
saves the customer money by not just throwing parts at an undiagnosed
problem .

Modern cars are too complicated. The idle used to be controlled by a
screw that stopped the throttle from closing completely.

[Colour Sergeant Bourne]

Post by Max Demian

Post by Ken Blake
I have a Mitsubishi Lancer 2003 which has low idle speed.
So low that it stalls unless I keep the gas on the peddle.
What causes that?

You're thinking backwards.  Think about what happens when you're at idle.
Something needs to happen to make the mixture more rich, and that could be
done in all kinds of different ways.  Some cars have an extra
injector just
for idle, some have software in the ECU that runs the normal
injectors more
rich, some have a gadget in the carb that is activated by engine vacuum.

   A total crock of shit Scott . Idle mix is NOT enriched , if
anything it's leaned out . I strongly suspect it's either an IAC or
the MAF sensor that's malfunctioning - IAC is most likely , and can
USUALLY be cleared up with being cleaned with carb spray . The best
thing for him to do is have one of the local parts stores run an OBDC2
scan . Just about every parts store does this for free . Makes sales
for them and saves the customer money by not just throwing parts at an
undiagnosed problem .

Modern cars are too complicated. The idle used to be controlled by a
screw that stopped the throttle from closing completely.

Yeah, I recall President Eisenhower mentioning how functional that
arrangement was during a Rose Garden press conference.

[Snag]

Post by Max Demian

Post by Ken Blake
I have a Mitsubishi Lancer 2003 which has low idle speed.
So low that it stalls unless I keep the gas on the peddle.
What causes that?

You're thinking backwards.  Think about what happens when you're at idle.
Something needs to happen to make the mixture more rich, and that could be
done in all kinds of different ways.  Some cars have an extra
injector just
for idle, some have software in the ECU that runs the normal
injectors more
rich, some have a gadget in the carb that is activated by engine vacuum.

   A total crock of shit Scott . Idle mix is NOT enriched , if
anything it's leaned out . I strongly suspect it's either an IAC or
the MAF sensor that's malfunctioning - IAC is most likely , and can
USUALLY be cleared up with being cleaned with carb spray . The best
thing for him to do is have one of the local parts stores run an OBDC2
scan . Just about every parts store does this for free . Makes sales
for them and saves the customer money by not just throwing parts at an
undiagnosed problem .

Modern cars are too complicated. The idle used to be controlled by a
screw that stopped the throttle from closing completely.

That complication has brought us more powerful and clean burning IC
engines too . There was a sweet spot in the late 90's and up to about
2010 , after that they started loading cars up with extraneous and IMO
unnecessary frills .

[Xeno]

Post by Max Demian

Post by Ken Blake
I have a Mitsubishi Lancer 2003 which has low idle speed.
So low that it stalls unless I keep the gas on the peddle.
What causes that?

You're thinking backwards.  Think about what happens when you're at idle.
Something needs to happen to make the mixture more rich, and that could be
done in all kinds of different ways.  Some cars have an extra
injector just
for idle, some have software in the ECU that runs the normal
injectors more
rich, some have a gadget in the carb that is activated by engine vacuum.

   A total crock of shit Scott . Idle mix is NOT enriched , if
anything it's leaned out . I strongly suspect it's either an IAC or
the MAF sensor that's malfunctioning - IAC is most likely , and can
USUALLY be cleared up with being cleaned with carb spray . The best
thing for him to do is have one of the local parts stores run an OBDC2
scan . Just about every parts store does this for free . Makes sales
for them and saves the customer money by not just throwing parts at an
undiagnosed problem .

Modern cars are too complicated. The idle used to be controlled by a
screw that stopped the throttle from closing completely.

Odd, that's what the IAC does in a TBI/PFI engine - allows air to bypass
the throttle body.

Anyway, in order to better control emissions, the last of the carbs
became too complicated. TBI/PFI simplified fuel delivery as well as
making it more accurate and, at the same time, providing better
atomisation/vapourisation. Carbs, dead and buried.