Variable RPM problem when engine is cold

[Brainmaze]

Hi,

I have a problem with my 3, when I start the car and the engine is cold,
I start to drive (normal driving), shift in 2nd, then if I release the gaz pedal a little bit, the RPM starts to vary itself from 3000 to 1000 rpm.

It's very annoying.

Already done on the car :
-Soldering on MAF wires (due to CAI)
-Second O2 sensor changed (OEM from dealer)
-Updated PCM (at dealer)
-MAF cleaning
-Throttle body cleaning

Do you have any idea on what can cause this problem ?

I repeat, as soon as the engine gets warm, the problem completly dissapears.

Thanks for your suggestions

P.S: Excuse my English, i'm from Quebec :chuckle

[Brainmaze]

no ideas ??

Thanks

[Donutz]

Are you certain its not the maf? With the car running gently move the harness. If your idle changes you likely have a bad wire.

Other than that, maybe a vacuum leak.

[Brainmaze]

the MAF seems to be OK, the idle doesn't change when I play with the wires...

how can I check for vaccum leak ?

thanks again

[Brainmaze]

I've found a new MAF harness/connector from a junkyard for free !
I'll get it soldered soon and see if that helps.

[Brainmaze]

maf connector is changed, throttle body cleaned again and the problem is still there, do you have any idea on what could be the problem ?

thanks again

[Zoom Zoom Boy]

maf connector is changed, throttle body cleaned again and the problem is still there, do you have any idea on what could be the problem ?

thanks again

Did they try changing out the Spark Plugs? What about the Ignition wiring? Even if the plugs look fine and are gapped ok, it is worth putting in a new set to see if the problem goes away. Sometimes even plugs that look fine and aren't visibly fouled can have issues with sparking.

[m_bisson]

the engine will idle higher automatically if it's cold in order to help bring the temperature up.

[Zoom Zoom Boy]

the engine will idle higher automatically if it's cold in order to help bring the temperature up.

Yah, but the OP has a bouncing throttle issue, not just high idle at cold temps. The idle should always be fairly stable, even if higher when cold. For instance, it shouldn't start out at 1,500rpm and then suddenly bounce to 300rpm and vice versa...

[m_bisson]

hmm... well this is a stab in the dark, but I had problems with my a/c compressor that caused the same thing to happen. It was the middle of the summer though, so the car was going between stalling and 1200rpm. The fix was to re-adjust the pressure of the freon or w/e they use for cooling.

[Brainmaze]

hmm... well this is a stab in the dark, but I had problems with my a/c compressor that caused the same thing to happen. It was the middle of the summer though, so the car was going between stalling and 1200rpm. The fix was to re-adjust the pressure of the freon or w/e they use for cooling.

could this be my problem even if I don't use the A/C in the winter ?

thanks again

[Default User]

Check your coils.
Sounds like a little moisture is getting in and disrupting your idle
Moisture dries up and goes away when motor is warm, hence idle is fixed.

[sas]

Such things should be detected by logging the engine parameters by professional equipment. All what was written before may take place. The throttle body is being warmed by coolant. I can add the throttle body position sensor.

[Donutz]

Holy smokes sas is alive!

[Brainmaze]

could it be a defective motor mount ? or the tranny ?

I've never had any CEL !

[sas]

Yes, you haven’t a CEL, but many errors are being registered only when engine is warmed, sensor’s errors must exist some time to be registered by pcm.
It still unclear, do you have an auto or manual. I suppose the TWM is the short shifter.
I don’t see how the manual transaxle can affect the rpm.
The engine mount can’t cause the rpm changing, but moving or strained harness can.
This version is looking very plausible except a link to the temperature.
You have this effect when slightly changing the pedal position, that is why I think
about erratic signal from pedal position sensor, throttle position sensor or problem with the throttle actuator.
Was changed second O2 sensor. There is a possibility that you have a weak cat.
Some cars (don’t know if Mazda too) have additional algorithm to detect misfires
from second o2 sensor. This algorithm measures the spike of oxygen.
But again, there is no CEL.
In another thread you asked about first o2 sensor. The first sensor with substandard heating element can cause such behavior.
Amateur equipment may shed some light on the problem but result isn’t guaranteed.
There is an example how to understand the readings of first O2 sensor.
http://i709.photobucket.com/albums/ww96/sas2000_album/o2sensor.jpg

[Prima Tech Aaron]

Did the throttle body get cleaned before the problem started?
If not clean it then after putting everthing back, Disconnect the battery for a few minutes, reconnect and test drive.

[Brainmaze]

Did the throttle body get cleaned before the problem started?
If not clean it then after putting everthing back, Disconnect the battery for a few minutes, reconnect and test drive.

it was cleaned after the problem appeared, I already disconnected the battery a lot of time and the problem stays..

[Brainmaze]

Yes, you haven’t a CEL, but many errors are being registered only when engine is warmed, sensor’s errors must exist some time to be registered by pcm.
It still unclear, do you have an auto or manual. I suppose the TWM is the short shifter.
I don’t see how the manual transaxle can affect the rpm.
The engine mount can’t cause the rpm changing, but moving or strained harness can.
This version is looking very plausible except a link to the temperature.
You have this effect when slightly changing the pedal position, that is why I think
about erratic signal from pedal position sensor, throttle position sensor or problem with the throttle actuator.
Was changed second O2 sensor. There is a possibility that you have a weak cat.
Some cars (don’t know if Mazda too) have additional algorithm to detect misfires
from second o2 sensor. This algorithm measures the spike of oxygen.
But again, there is no CEL.
In another thread you asked about first o2 sensor. The first sensor with substandard heating element can cause such behavior.
Amateur equipment may shed some light on the problem but result isn’t guaranteed.
There is an example how to understand the readings of first O2 sensor.
http://i709.photobucket.com/albums/ww96/sas2000_album/o2sensor.jpg

yes I have a manuel transmission...
I'll probably get the car to the dealer for a investigation on it, but i'll wait to see if it gets better this summer whit higher outside temp.

[Zoom Zoom Boy]

Has anyone ever tried to simply change the spark plugs?

[n00bMeiSter]

not to highjack the thread, but what is "CEL"?

[aris]

but what is "CEL"?

Check Engine Light

[sas]

The management of the engine is too complicated nowadays.
I think the visit to an experienced diagnostician is the best idea.
They can spot faulty or suspicious part even without hunting for this specific moment.

[Brainmaze]

yes i'll take it to the dealer sometime,

and also the symptoms completely disapear when I press the clutch, don't know if it can help

[n00bMeiSter]

Check Engine Light

Ah, thanks :)

[sas]

This fact slightly changes the priority.
It’s hard to say without looking on the car, Your feelings are very important. It might be a misfiring.
The cold engine has a less compression plus the cold mixture is less flammable.
On the second speed you must feel the gaps in engine power. Usually misfiring happens when you are accelerating but can to be when you have a lean or poor atomized mixture. In closed loop it will be corrected automatically with throwing the CEL, whereas with engine temperature below 50C you could have the described symptoms.
Lean mixture? Small leak from purge valve can do it . When you start the cold car the evaporative system pumps the fresh air inside of the fuel tank to check air leaks.
Since time ,if this leak is small, it will not affect on the emission control system when there will be the vapors of gas only.
Practically, the leak less than 10-12 percents of purge valve capability is invisible for emission system.
I have so much of different versions.
I usually observe the car a long time before I try to undertake something.
Nothing speaks that there is a potential harm for the engine.
You can wait some time to collect more information.

[Brainmaze]

This fact slightly changes the priority.
It’s hard to say without looking on the car, Your feelings are very important. It might be a misfiring.
The cold engine has a less compression plus the cold mixture is less flammable.
On the second speed you must feel the gaps in engine power. Usually misfiring happens when you are accelerating but can to be when you have a lean or poor atomized mixture. In closed loop it will be corrected automatically with throwing the CEL, whereas with engine temperature below 50C you could have the described symptoms.
Lean mixture? Small leak from purge valve can do it . When you start the cold car the evaporative system pumps the fresh air inside of the fuel tank to check air leaks.
Since time ,if this leak is small, it will not affect on the emission control system when there will be the vapors of gas only.
Practically, the leak less than 10-12 percents of purge valve capability is invisible for emission system.
I have so much of different versions.
I usually observe the car a long time before I try to undertake something.
Nothing speaks that there is a potential harm for the engine.
You can wait some time to collect more information.

Thanks a lot for your help, it is really appreciated !

I forgot to mention that I replaced the spark plugs last summer with Bosch "cheap" ones, but my problem was present before I replace the spark plugs...

So you theory would be a bad or a leak in the Purge Valve ?
Or maybe bad coil packs which should throw a CEL normally...(I had this problem on my Protege and the CEL was flashing all the time) ?

I want to get as many information possible before to get the car to the dealer, I don,t want to spend to much money just for troubleshooting :)

thanks again

[sas]

It depends on what you feel. Initially, I imagined just a variable rpm like if you play with the gas pedal. Changes of rpm under load in such wide ranges without CEL can be done only legally or almost legally. The legal way is to close the throttle body. It can be happen if throttle body receives the signal to close from pedal position sensor.
“Almost legal” is when throttle body receives the command to close from protecting systems like the temperature monitor for catalytic converter, or the position of throttle position sensor was mistakenly interpreted by PCM as “closed” and was started the fuel cut mode.
I considered it in context of relations to the temperature. I never took apart these sensors on mazda3, from wiring manual they are the same, the bridge of two potentiometers. If the sensor is dirty or worn the work of sensor can depend on the temperature. There enough a one short pulse to initiate the fuel cut mode, whereas for the CEL the wrong signal must be active for 10 seconds. One more thing, if throttle is seeking the right position, these modal systems are very sluggish if there is a bad contact or a jam they are bouncing back and force.

Now I think it’s a loss of power because the engine works fine without load on the transmission. The ordinary misfiring, it’s possible, but I was looking a way why it isn’t happening in moment of hard acceleration when the mixture has a higher density.
I stopped on the purge valve just because the purge valve is opened almost all time
and is completely closed only after any acceleration for short time 10-40 seconds.
The exact moment when you have this problem.
The rpm variation is so wide that I think there is something more serious,
like broken wire, throttle body, cold or leaking O2 sensor, or floating one of the reference voltages in PCM.
There is a bunch of different sensors and valves and don’t forget there is an electronic part. It’s a pain to check the all my multimeter or by code reader.
What you can?
You can check if there are wires or harnesses in engine compartment which
can be stretched when engine moving a bit forward. Reconnect the PCM connectors and connector of pedal position sensor. The coolant level must be higher than the minimal mark. Do the visual check of the intake manifold and connected to it hoses. Listen the exhaust manifold for leaks. Clean the spark plug coils, look if there are carbon traces. Yes, theoretically the misfiring should be detected, but used algorithm is effective when you accelerate and less effective under small loads, when transmission helps to spin the engine.
If you want any actions…
The check of O2 sensor by standard multimeter is useless in you case.
You soldered the maf and this check shouldn’t be a big problem.
This is the pinout for MAF harness.


_____|====|______
|..E…D…C…B…A|
A – MAF supply voltage
B – MAF ground (black wire)
C – MAF output
D – IAT ground
E – IAT output
Securely connect the negative wire of the multimeter to the chassis.
MAF is connected, engine stopped, the ignition key is in ON position.
Set the measurement range to 20V DC or nearest what you have on your instrument.
By positive multimeter’s probe measure the voltage:
1: Terminal A – (12.5 – 13.5 V)
2: Terminal B – (0 – 0.1V)
shake the harness and watch if voltage is going up. There must be a pure 0,
I wrote 0.1 just because some multimeters are too sensitive to ambient noise.
If voltage is high, there is the bad maf ground wire.
3: Terminal C – (0.6 – 0.8V)
4: Terminal E Voltage on this terminal depends on the ambient air temperature
0C – 3.43V 20C – 2.38V
you can recalculate the voltage for current temperature by formula
V= 3.43- Tcurent(C) * 0.0525
The accuracy isn’t important, better, shake the harness and look if readings change. Voltage is rising it’s the bad ground wire D, dropping – the bad wire E.

5: Start the car and warm the engine
After the idle rpm is stabilized, measure the voltage on terminal C.
Must be 1.2V–1.5V.
6: Set the engine speed to 2500-3000 rpm
Voltage on terminal C must be 2 – 3volts
7: Gradually increase the rpm and be sure that the voltage rises and isn’t
exceed 5volts.

It is a very approximate test. Really, the PCM converts this nonlinear voltage into the air ratio via a calibration table.
Now you know all what I know.
I have a sense that I just wrote a book.

[Brainmaze]

It depends on what you feel. Initially, I imagined just a variable rpm like if you play with the gas pedal. Changes of rpm under load in such wide ranges without CEL can be done only legally or almost legally. The legal way is to close the throttle body. It can be happen if throttle body receives the signal to close from pedal position sensor.
“Almost legal” is when throttle body receives the command to close from protecting systems like the temperature monitor for catalytic converter, or the position of throttle position sensor was mistakenly interpreted by PCM as “closed” and was started the fuel cut mode.
I considered it in context of relations to the temperature. I never took apart these sensors on mazda3, from wiring manual they are the same, the bridge of two potentiometers. If the sensor is dirty or worn the work of sensor can depend on the temperature. There enough a one short pulse to initiate the fuel cut mode, whereas for the CEL the wrong signal must be active for 10 seconds. One more thing, if throttle is seeking the right position, these modal systems are very sluggish if there is a bad contact or a jam they are bouncing back and force.

Now I think it’s a loss of power because the engine works fine without load on the transmission. The ordinary misfiring, it’s possible, but I was looking a way why it isn’t happening in moment of hard acceleration when the mixture has a higher density.
I stopped on the purge valve just because the purge valve is opened almost all time
and is completely closed only after any acceleration for short time 10-40 seconds.
The exact moment when you have this problem.
The rpm variation is so wide that I think there is something more serious,
like broken wire, throttle body, cold or leaking O2 sensor, or floating one of the reference voltages in PCM.
There is a bunch of different sensors and valves and don’t forget there is an electronic part. It’s a pain to check the all my multimeter or by code reader.
What you can?
You can check if there are wires or harnesses in engine compartment which
can be stretched when engine moving a bit forward. Reconnect the PCM connectors and connector of pedal position sensor. The coolant level must be higher than the minimal mark. Do the visual check of the intake manifold and connected to it hoses. Listen the exhaust manifold for leaks. Clean the spark plug coils, look if there are carbon traces. Yes, theoretically the misfiring should be detected, but used algorithm is effective when you accelerate and less effective under small loads, when transmission helps to spin the engine.
If you want any actions…
The check of O2 sensor by standard multimeter is useless in you case.
You soldered the maf and this check shouldn’t be a big problem.
This is the pinout for MAF harness.


_____|====|______
|..E…D…C…B…A|
A – MAF supply voltage
B – MAF ground (black wire)
C – MAF output
D – IAT ground
E – IAT output
Securely connect the negative wire of the multimeter to the chassis.
MAF is connected, engine stopped, the ignition key is in ON position.
Set the measurement range to 20V DC or nearest what you have on your instrument.
By positive multimeter’s probe measure the voltage:
1: Terminal A – (12.5 – 13.5 V)
2: Terminal B – (0 – 0.1V)
shake the harness and watch if voltage is going up. There must be a pure 0,
I wrote 0.1 just because some multimeters are too sensitive to ambient noise.
If voltage is high, there is the bad maf ground wire.
3: Terminal C – (0.6 – 0.8V)
4: Terminal E Voltage on this terminal depends on the ambient air temperature
0C – 3.43V 20C – 2.38V
you can recalculate the voltage for current temperature by formula
V= 3.43- Tcurent(C) * 0.0525
The accuracy isn’t important, better, shake the harness and look if readings change. Voltage is rising it’s the bad ground wire D, dropping – the bad wire E.

5: Start the car and warm the engine
After the idle rpm is stabilized, measure the voltage on terminal C.
Must be 1.2V–1.5V.
6: Set the engine speed to 2500-3000 rpm
Voltage on terminal C must be 2 – 3volts
7: Gradually increase the rpm and be sure that the voltage rises and isn’t
exceed 5volts.

It is a very approximate test. Really, the PCM converts this nonlinear voltage into the air ratio via a calibration table.
Now you know all what I know.
I have a sense that I just wrote a book.

thanks that's great, i'll do a little visual inspection like you mention.

[sas]

I’m glad if it will be helpful. Here were a few things unclear to me. It seems to me
that the change from 3000rpm to 1000 at 2nd gear is a little bit more then “annoying”.
Maybe we speak here about worn clutch?
Second thing, it’s unclear, how long you stay in 2nd gear, possible we use a different driving technique. For me 3000 rpm it’s a highest revs at second gear when I shift into 3rd. Your post can be understood as you already have 3000rpm when you just shifted into second gear. I don’t believe that someone kick a cold engine so hard.
It’s unclear but interesting for diagnosis, do revs return back to 3000 by itself, by pressing the gas pedal farther or by restoring the pedal position.

[Brainmaze]

here is a video of the problem :
we see a good example at about 55 seconds...

http://i101.photobucket.com/albums/m49/Brainmaze/th_P1040798.jpg (http://s101.photobucket.com/albums/m49/Brainmaze/?action=view&current=P1040798.flv)

It doesn't change from 3000rpm to 1000rpm but only a few hundred of RPM
I today I felt a little lack of power and little hesitations on acceleration (even when the engine was warm)

[sas]

Diagnosis via internet…uhh… I remember a forum, people were complying about the same noise, it was epic thread in 15-20 pages until one of them had recorded his noise.
In result, all of them had absolutely different noises.
It’s absolutely another picture then I imagined. The first O2, at idle, works normally.
The MAF harness for the vibration you already checked.( If only it wasn’t on a cold car. )
Most like it’s a kind of misfiring because a small leak in the intake manifold or clogged injectors. Seems to me I heard strange noises at the end of acceleration, apparently it’s a noise of released gas pedal.
Try to clean injectors. The sticking purge valve it is possible too, I think you will have the CEL at the end. Or you can check it by plugging the hose between manifold and valve, for short test drive.

[Brainmaze]

this morning, when I was on 1st gear and press the gaz pedal to accelerate, the car has a moment where "nothing" happened like if the power disapeared !!
I think it's getting worse, maybe a CEL will appear soon ! I'n fact, I hope ! :)

[sas]

This weather is favorable for all types of misfiring.
I re-watched the video.
I can hear here at 55sec a three claps. I’m unsure what it is, a blank cycles, untimely ignition or outside noise.
Pay attention on it, for me, it sounds as a typical empty stroke.

[Brainmaze]

the sound at 55sec is probably just my camera...
and what is an empty stroke ?

thanks again ;)

[sas]

He.. “Empty stroke”.. I think it’s my invention. I meant the ”power stroke” when the mixture wasn’t burned, you can hear the pressurized air exiting from cylinder and there a weak bang instead of the full-blooded blast.
I just wanted you to notice it if this sound is real.
At this moment, I’m more inclined to the injector’s theory.

[Brainmaze]

ok i'll do another test tomorrow morning and let you know

[Brainmaze]

finally there is no sound...

I went to the garage today to have my MAF/IAT wires resoldered, i'll do another tomorrow morning to see if the problem persists

[sas]

The clogged injector version has the only one small weak place. I don’t know how it could coexist with normal engine start. Maybe you noted a worst cold start.
Why injectors. Most of the units and sensors were excluded because you have a normal acceleration and a stable idle. My opinion it is not a last verdict it’s just an opinion.
As I said before ,at acceleration, a bit earlier after the rpm are stabilized or when you slightly release the gas pedal the purge valve is closed completely, and there is no added vapors of the gas from the fuel tank.
If the purge valve works correctly, these vapors are the ready to use well atomized and mixed with air mixture, even more concentrated. Possible, that the injectors are poorly atomizing the fuel and the vapors from fuel tank are compensating the shortage of atomized mixture. If the acceleration wasn’t hard the purge valve will be closed somewhere 8-15 seconds. Look if these symptoms will disappear since 10-15 seconds after you released the gas pedal.
From amount of the atomized mixture is highly dependant the speed of the heat spreading
and as result ,the speed of combustion. There is the interesting video.
http://www.youtube.com/watch?v=UvmBLqjaZxY
The open flame there, it’s the combustion of the fuel which wasn’t mixed with the air.
It burns too late and doesn’t perform any work. Most effectively the work is being performed somewhere at 1/7 of power stroke when the piston just started to move.



Now about the CEL.
To turn on the CEL you need in two CONSECUTIVE driving cycles. In the first driving cycle will be stored the “pending error”. If the same error wasn’t registered in the next driving cycle ,the pending error will be restored. After the CEL appeared the error will be stored in DTS memory and since that time you will have the CEL every time when error was registered by PCM. I think you must have the “Too reach at off-idle” error.
To cause it you must give a time to the PCM to correct the Long Term Fuel Trim.
The LTFT is been corrected every 30 seconds, so you should drive with this problem no less then 30 seconds ,maybe more, until the LTFT will be corrected in the second time.
Then, you have to repeat this trick in the next trip. Try it.

[Brainmaze]

the problem is still there after the resoldering of my MAF Harness :(

[sas]

Sorry for my persistence.
And again, I watch the video. I wrote the time incorrectly. There are three knocks at
53-54 seconds and it’s not a camera. After those knocks the needle drops.
I’m confident on 99 percents that these are knocks and the PCM postponed the timing advance.
Pleeease hear it.

[Brainmaze]

Sorry for my persistence.
And again, I watch the video. I wrote the time incorrectly. There are three knocks at
53-54 seconds and it’s not a camera. After those knocks the needle drops.
I’m confident on 99 percents that these are knocks and the PCM postponed the timing advance.
Pleeease hear it.

ok so I'll need a new PCM flash ?
or try to reset it again by unpluging my battery ?

thanks again, I really appreciate your help

[sas]

No. If the knock is really exist. Do not play with it, how I recommended to cause the CEL.
You have it on a cold engine and it can be caused by lean mixture or by early timing advance. The timing advance dependant on the RPM level, engine temperature, particularly on the MAF readings, and on the position of the CKP (crankcase position sensor).
You do not have the ability to check them yourself .
The lean mixture, in your case, can be caused by sticking purge valve, clogged injectors, or maybe by leak in the intake (chances are low, because the idle is fine and no errors).
The best way, is to be assured that you really can hear the knock and to bring the car to the dealer with a specified complaint.

[Brainmaze]

No. If the knock is really exist. Do not play with it, how I recommended to cause the CEL.
You have it on a cold engine and it can be caused by lean mixture or by early timing advance. The timing advance dependant on the RPM level, engine temperature, particularly on the MAF readings, and on the position of the CKP (crankcase position sensor).
You do not have the ability to check them yourself .
The lean mixture, in your case, can be caused by sticking purge valve, clogged injectors, or maybe by leak in the intake (chances are low, because the idle is fine and no errors).
The best way, is to be assured that you really can hear the knock and to bring the car to the dealer with a specified complaint.

ok so do you suggest me to try some "Injector cleaner" first ? maybe it could help a bit
or a real injector cleaning by the dealer ?

[sas]

Of course, I have some instruments and tools to check what is wrong with the car more precisely. With my dealer’s prices , possible, if I was you I’d cleaned the injectors by cleaner, but I afraid that there could be a “systematic” problem which can be detected only by reading the engine parameters.

I think I understand why you can’t hear this noise, use a headphones. You will know
what about I’m speaking.