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Last seen: 1 year 9 months ago
Joined: 06/27/2014 - 23:10
Evo 8 idle how i fixed it
**** I built my own patch harness ****
Since I first put the AEM Infinity on the EVO my idle has always been random.  I could dial in the idle then on then on restart the idle would be completely off.  I was never able to get my car to idle lower than 1600rpm other wise it would just stall on me.  This lead me down a crazy path.

1. Rebuilt the throttle body - No change
2. Brand new OEM IAC Valve - No Change
3. OEM Intake Manifold - No Change
4. Replace all Gaskets related to intake manifold and throttle body - No Change
5. Spend hours adjusting the BISS and the tune - No Change

So as a last resort, I pull the IAC valve out to see what it is doing.  When the motor would "park" it extended the plunger to the max.  When the valve was out of the TB it was not an issue.  Once the IAC was in the TB and the park happened I could hear the IAC clicking.  This was the gear drive on the inside skipping teeth.  Changing the "Idle Stepper max steps" did not affect how far the "park" would drive the plunger.

So in order to fix the skipping teeth issue I wanted the "park" to bottom out the plunger.  To accomplish this I needed to move:

C1-69 to C1-70
C1-70 to C1-69
C1-71 to C1-72
C1-72 to C1-71

This will now drive the IAC in the opposite direction.  So when the "park" function happens it now bottoms out the IAC.  I then needed to check "Idle Airflow Invert".

After this was completed I am now able to get the car to idle at 1000rpm, and start and idle every time.

How I was testing(Not the word of god, just some back woods testing):

1. Pull the idle motor out of the throttle body, leave it hooked up to the connector.

2. Put the car to the on position, wait 20 seconds and measure the position of the plunger or take a pic with your phone.

3. Remove the key from the car, wait 20 seconds and measure the position of the plunger or take a pic with yoru phone.

4. If the plunger moved to the bottom of the idle motor when the key is off, then everything is configured correctly.

 -- You will need to adjust the max limits, ignore further steps

5. If the plunger extends all the way out this could be the source of your problem.

-- Measure the max length of the plunger extended all the way out, then measure the depth of the hole that the plunger sits in.  If the lenth of the hole is less than the length of the plunger then your idle motor is hitting a mechanical stop, and the idle motor could be skipping teeth screwing up the position the aem thinks it has the motor in.

-- This will require the wire swap, the wire change will simply drive the motor in the opposite direction.  So when the park command hits, it shoudl bottom out the plunger to the idle motor.

6. Find the max value.  Using the measurements from the hole and the plunger, start to adjust your Idle base Settings until the plunger is at the max depth for the hole.  You now have your max Idle base setting.

7. Turn the car completly off, pull the key out waite 5min, put the key back in the car and watch the idle motor again.  Did everything work as expected?  Did the plunger go to the position it was supposed to?

-- If so you are ready to put the motor back in the car, pull the key out and put the idle motor back in the car.

-- If not redo steps 6 and 7 until you are good.

8. Everything is back in the car.  Start it up and tune your idle.  The only reason to check invert airflow is so that a lower number in the Idle Base Setting table will result in a lower idle, and a higer setting will result in a higher idle.


Other items, you might have to much PID going on in your idle.  For me on the Evo 8 I am running p=.001, I=.005, d=.002.  For the ignition it is p=.000, I=.00, d=.010.  So the PID setting might be to agressive.

Last seen: 1 year 9 months ago
Joined: 06/27/2014 - 23:10
My current setting specific

My current setting specific to the video above.

Last seen: 3 years 5 months ago
Joined: 06/05/2014 - 15:56
I tried this fix on my can

I tried this fix on my car and I still cannot get my idle below 1500rpm. Now me not being a professional tuner, I thought maybe I was just missing something....I finally was able to bring my car to my tuner and the car made great power, but my tuner still couldn't get the idle lower than 1500rpm....anytime he made an adjustment to lower the idle the car would die instantly. Anyone have any input? 

DP's picture
Last seen: 3 years 4 months ago
Joined: 04/13/2015 - 16:27
I have been struggling with

I have been struggling with the idle and randominess of it as well. Glad to find this post....Thx for the write up Boz!

Last seen: 2 years 7 months ago
Joined: 07/30/2016 - 05:34
Hello TheBoz,

Hello TheBoz,

Are you using a P&P harness?

Can you report how switch the pins from ISCV connector side...not  ecu connector side?


Thanks a lot

Last seen: 11 months 1 week ago
Joined: 05/21/2015 - 05:33
Ive tuned EVO8 with P&P

Ive tuned EVO8 with P&P harness without any issues.  Idles great everytime.  

Last seen: 16 hours 39 min ago
Joined: 08/26/2014 - 08:51
I've done 2 evo's and both I

I've done 2 evo's and both I was able to get to idle properly by setting the idle stepper max and pulses so that the idle motor wouldn't over extend itself.  I really like TheBoz idea of switching the wires so that when it goes into the park position it parks itself against the IACV instead of extending out.

Last seen: 5 months 4 weeks ago
Joined: 08/28/2014 - 18:59
I inverted the wires as

I inverted the wires as discussed in the opening post, and at least in my specific case the idle is much more consistent from start to start. I have very aggressive cams and prior to this mod had to maintain idle somewhere in the 1200 rpm's in order not have stalling issues. Sometimes I would start the car and it would idle at 1200 rpm's and at the following start up it would be somewhere in the 1000 rpm range. After the wire swap, I have dialed it down to 1050 - 1150 and it is constant from start to start. 

Last seen: 4 days 7 hours ago
Joined: 09/16/2016 - 18:02
Anyone who has been able to

I was able to get my idle stable after configuring the Infinity with 147 Idle Stepper Max Steps. This is without reversing the idle motor park operation.

Last seen: 11 months 1 week ago
Joined: 05/21/2015 - 05:33
Those are the wrong pins for

Those are the wrong pins for EVO8 stepper motor.





Last seen: 1 year 2 months ago
Joined: 06/06/2014 - 09:31
Those are the right pins if

Those are the right pins if you're using a Series 7.

Last seen: 6 months 1 week ago
Joined: 03/03/2019 - 16:59
The OE IAC looks like this

The OE IAC looks like the link below and was not controllable for me. Was never able to control it. Idle position was at max almost 95% of the time no matter what I did. Sometimes I would get it to idle it would be great until I shut it off and then restarted the vehicle. Idle position was stuck at 100 99% of the time.


The one I ended using was this one...


I was able to use any and all commands to control it vs the other one and my idle is 100% tunable and reacts to all the commands. I was on the edge of switching the wires around according to this thread unti; I found an alternate IAC. If anyone has trouble tuning idle on their EVO, try this IAC version from Oreilly Auto Parts. Part #AC254. It actually has a Mitsu symbol on it.

Last seen: 4 months 2 weeks ago
Joined: 05/08/2019 - 22:03