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Help setting smooth idle with Mitsubishi EVO ISC stepper valve


TnF

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So i've basically done a complete conversion on a JDM EVO 8MR with a PnP Link G4+. Did some basic tuning and everything is mostly OK. It's based on the base map provided to save some time.

The engine has an aftermarket Magnus intake manifold and a Boomba 75mm TB. It has integrated "manifold" for the factory IAC valve but no fine idle screw adjustment. It has only a set screw that sets the closed position of the throttle body butterfly valve.

IAC has been replaced with a NEW genuine Mitsubishi factory IAC valve (evo 9 style with exposed spring) as after i borrowed a known working one i noticed the existing one was not traveling the same range (since i know it got stuck at some point and was unjammed after i cleaned it).

Now with the new valve and base map settings for it i have an oscillation.

I know it's caused by the ISC settings (closed loop) since i can see it in the runtime values and if i disconnect the valve idle is smooth.

Setting base bypass was done before by removing the IAC and jamming a rag in to set the min idle airflow. This should be set 50-100rpm below the desired idle value. I've noticed this engine wants to idle a little higher to be smooth due to the cams and cam adjustment used.

Now i just need an example procedure on how i can tune these settings before i quit and run open loop instead lol.

I have lots of questions. Example when the ISC is reset (on key off) does it close the passage fully, open the passage fully, or goes to a set step position?

If i want to disable the control and set the ISC fully closed so i can set the base idle adjustment how can i do it? If i knew the position (my question above) i can maybe just disconnect it before starting the engine and set it that way.

Please point me to the right direction :)

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9 hours ago, TnF said:

I have lots of questions. Example when the ISC is reset (on key off) does it close the passage fully, open the passage fully, or goes to a set step position?

The reset at key off procedure is to step the valve fully open, then back closed a fixed value, from memory it is 50 steps closed.  When the ignition is switched on again for the next start up then it moves to the correct base position for the current temperature minus the start up step.

 

10 hours ago, TnF said:

If i want to disable the control and set the ISC fully closed so i can set the base idle adjustment how can i do it? If i knew the position (my question above) i can maybe just disconnect it before starting the engine and set it that way.

Set to open loop and put a really large number in the base position table - say 700.  Make sure the max clamp is above this value.

 

Need to see a log of the oscillation really, usually stepper motors are too slow to be the sole cause of an oscillation so you may have something else fighting you.  

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  • 2 months later...

Sorry for the late reply, i forgot to reply back, but the processes was much much easier after i got into it practically.

I only needed to setup the open loop correct and then made very minor adjustments to the closed loop.

Did my best for emissions but the cams are just too big;p Average AFR was ok but wasn't combusting well enough so hydrocarbons were seriously bad. That's why you should get the MIVEC engine instead :p

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