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post #1 of 21 (permalink) Old 09-02-2015, 09:34 PM Thread Starter
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Angry The Super Annoying Idle Issue

Let me just start off by saying if you think this isn't an issue, leave now because I'm telling you that it is. The idle will jump well above 1,000RPM and then dip back down to 600RPM. Not only is it super annoying, but I've got the data to back it up.

You can leave the "try resetting the battery" and "It's just relearning the idle" comments out as well.

Some info about the car. It's 2006 Mazda 3 2.3L with ~126K miles and an AEM CAI with dryflow filter. Problem started happening a couple months ago and it's intermittent. Can't seem to cause it by "doing" anything.

NOTE: I have ZERO codes. No check engine light. Nothing.

FIRST: What is the issue?

The idle can be normal at times, but at others completely jumps around and drives me absolutely nuts.

*VIDEO 1*
*VIDEO 2*

Regular idle.

Fluctuating idle.

Idle after new MAF sensor.

Fluctuating idle after new MAF sensor.


"But what does all that data mean?"

*SPARKADV should be around ~9degrees. Anything higher means the spark happens before it should, anything lower (negative) means it's igniting after it should.

*LONGFT1 and SHRTFT1 are long/short fuel trim for bank 1. (4cyl only have 1). Anything positive means the car is adding more fuel to compensate for a lean mixture. Negative means reducing fuel to compensate for a rich mixture.

*TP is throttle position, as a %. (100% = WOT)

*LOAD_PCT is this complex formula:
Quote:
LOAD_PCT =
[current airflow] / [(peak airflow at [email protected] as a function of rpm) * (BARO/29.9
2) * SQRT(298/(AAT+273))]

Where:

STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg BARO,
SQRT = square root,
WOT = wide open throttle,
AAT = Ambient Air Temperature and is in °C Characteristics of

LOAD_PCT are: Reaches 1.0 at WOT at any altitude, temperature or rpm for
both naturally aspirated and boosted engines.

Indicates percent of peak available torque.
Linearly correlated with engine vacuum
Often used to schedule power enrichment.


SECOND: What have I done?
  • Cleaned throttle body
  • Cleaned intake
  • Replaced MAF
  • Replaced purge solenoid
  • Checked EGR
  • Checked MAF wiring (seems okay)

THIRD: What next?
  • A/F oxygen sensor ($100)
  • Check vacuum lines
  • PCV valve ($6)
  • Fuel pump ($400)

FOURTH: Discussion.

In the first two charts I saw a big increase in MAF readings, so I assumed my MAF was bad, since the MAF is the first part of the entire system. Not only was the MAF fine to begin with, but the amount of air seen by the MAF is related to how much the engine is sucking in, so I was wrong to think that the MAF was bad anyways.

I have posted a couple times in the local Mazda Facebook groups, but it seems this problem is a bit much for the average social media browser to want to look into.

Any help is greatly appreciated.


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post #2 of 21 (permalink) Old 09-03-2015, 10:40 AM
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I have this same issue on my '09 2.0L. Idle goes a huntin' some times and it seems to be random as to when it happens and when it doesn't. I've adopted regularly cleaning out the TB (which you've done) because mine got to the point of stalling out the car coming to a stop (ATX).

I will say I noticed the hunting got more severe after I installed my CAI. By that I mean it happens no more frequently, but when it does the spikes are higher in magnitude than they were with the stock intake.

My 2cents - stop caring and live with it. The computer is trying to find the correct A/F ratio and your CAI only makes things more difficult. It probably is directly related to some ambient condition that matters to the computer but not anything significant enough for us to pick up on.

I would not dump any more $$ into this until its significantly impacting the performance or drivability of your car.

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post #3 of 21 (permalink) Old 09-03-2015, 11:43 AM
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I don't know enough about engines' computers to really know. Having those logs is definitely helpful to see everything is shifting around.

What I do not know however, is what all sensors are used to adjust idle. Something is starting it, and that is causing a chain reaction of it to keep going.

I had a idle bounce when I changed my throttle body to one that had a knife edge, and went back and it acted normal.

I can't say if it's the o2, MAF, or what, but something is giving a false reading, and causes the "noise" to begin, and it of course continues to get worse as it has to start chasing its tail to steady out the idle.

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post #4 of 21 (permalink) Old 09-03-2015, 03:39 PM
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The trims look a little odd... in one graph they are high the next they are ok and the next they are high again and he next low... just an observation ... I had something similar happen to me and it was related to the car trying to heat up the secondary 02 sensor... it would generate a CEL though - are u seeing any pendng cel's? = thought maybe the 02#2 is a bit dodgy and the ecu is responding by trying to warm it up = shoot in the dark

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post #5 of 21 (permalink) Old 09-04-2015, 06:38 AM Thread Starter
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Today I had this thought to put my stock intake back in and just see, for whatever reason, if that clears up the idle issue. After installed the stock intake and resetting the ECU the car definitely feels a little nicer when driving around, and the idle was fine, but I'm going to have to test it for some time to see if that issue comes back.

I was doing some reading about intakes having an "air-straightener", and our stock airbox actually has one in it. I was pretty surprised by this, as people will buy them for their aftermarket intakes to produce smoother MAF readings.

If it IS the AEM intake, then I'll be puzzled, but at least satisfied that I found the solution. I'm also considering doing a Sea Foam treatment. Lots of people use it for minor idle issues, and that's what this seems like.

Not sure if this means anything much, but here's the idle after reinstalling the stock airbox.


For comparison here's the same picture of the idle on the AEM intake and MAF.


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Last edited by Brado Bear; 09-05-2015 at 12:08 AM.
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post #6 of 21 (permalink) Old 09-04-2015, 12:35 PM
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Look at the fuel trims ... That tells the story ....


Sent from my iPhone using Tapatalk

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post #7 of 21 (permalink) Old 09-04-2015, 05:46 PM Thread Starter
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Quote:
Originally Posted by okellyr View Post
Look at the fuel trims ... That tells the story ....


Sent from my iPhone using Tapatalk


It's not adding the 7% of extra fuel, I see, but would you mind elaborating a little further?

Actually, the only thing that looks way different is the long term fuel trim, which if I understand correctly is the long term adjustments which might have just reset from the battery disconnect.


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post #8 of 21 (permalink) Old 09-05-2015, 08:22 AM
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Quote:
Originally Posted by Brado Bear View Post

I was doing some reading about intakes having an "air-straightener", and our stock airbox actually has one in it. I was pretty surprised by this, as people will buy them for their aftermarket intakes to produce smoother MAF readings.

Yes I've learned this recently as well. The cork sport intakes have an "air straightener" in them... At least the one I picked up for my mz5 2.5L has one.

The bends in the intake do the best they can to have the air flow through smoothly, and not tumble, but perhaps some other condition was causing air to get turbulent at times.

Very interested to see if it comes back after the relearn.

'09 3i|Injen CAI|TB Mods|Nighthawk Sports|Spyder Fogs

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post #9 of 21 (permalink) Old 09-06-2015, 03:22 AM
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the normal ltft should be somewhere between -3 and +3 ... + 7 ltft indicates that either there is a leak or that the MAF is under measuring the air flow which throws of the fueling calcs and results in the addition of fuel to maintain the targeted AFR ( 14.7)



You are spot on a battery reset would 0 out the LTFT. And it would be interesting to see what he ltft is after a few days

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post #10 of 21 (permalink) Old 09-06-2015, 04:22 PM
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I have an aem Cai with a dry flow no issues if that helps any np idle issues

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