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EVO 9 2.1 Build DBW Idle Issues

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I need assistance with an idle issue I'm having on an Evo 9. It's a 2.1 build, 272 cams, with a JMF Drag intake manifold, dual 1700cc injectors, and an 82mm bosch DBW throttle body running on AEM infinity. Idle won't come down to the target idle of 1100 rpm, even with large adjustments to timing and the VE table. No vacuum leaks are present, and the system was smoke tested. Currently, the idle is around 1300-1400 rpm with all the negative idle feedback possible. Let me know what other information would be helpful to guide me in the right direction.

Thank you

Hi. Have you applied special coating to seal the gap between TB and TB blade? Sometimes people remove it thinking it's dirt but that's there for exactly that reason- to eliminate the gap and avoid excessive air flow. Considering the large size of the TB you might be getting too much air through the gap at idle.

The other thing that cought my eye is TB size. To me 82 mm is overkill. That can cause all sorts of problems with engine running not smoothly. I'm using 74 mm TB on my 2.4L engine up to 7400 RPM and that's perfect in terms of helping the turbo to spool up and making good power up top.

I haven't removed any coatings from the TB. I think you're right that the 82mm TB is causing issues, but I have seen other builds get it to work properly. I placed an order for a 74 mm TB to see if that corrects the issue. I'll report once the new one is installed. Thank you!

Aftermarket TBs usually come without any coating, it needs to be applied as on OEM TB.

Another question is why did you choose such high idle RPM? 2.1L Evo 9 engine with mivec should be idling at 900-950 RPM very smoothly...

Shota I think he's saying he's tried to close the throttle body all the way and the idle is still higher than he wants it to be, despite the vehicle not having vacuum leaks. Is that correct OT?

An 82mm throttle should be able to restrict airflow sufficiently to shut the engine off unless there's a leak, or something preventing it from closing. I would verify that the ECU is actually driving the throttle to a fully closed position. You may need to hold the plate shut while calibrating the closed position to avoid losing part of the range of motion.

Mike, I thought the target RPM set at 1100 and actual is 1300-1400. That is why I thought even 1100 is kind of too high to me. In my experience 900+950 RPM at idle should do the job perfectly.

Mike, I can push the throttle body closed, and the car stalls along with blocking off the inlet, so I know it's only getting air through the TB. I've tried holding the plate shut when calibrating in the wizard, but it seems the resting position of the plate is still too open. Shota, as for the 1100 rpm target, I was just trying to get to a steady idle baseline where I could work to get the car to idle lower once I cleaned up the VE table and ign map. So, at the moment, there's no chance I can get to the 950 range until I get closer to the current target without maxing out the idle FB.

One other thing- we didn't talk about bypass bolt... Any changes when it's rotated?

In Infinity Tuner, what is the value of DBW_Target [%] when you are in idle control?

Have you tried adjusting the "Idle Base Position" table for a lower value at your target RPM -- I think this is probably the key

-- but I've never used DBW with an Infinity ECU. BTW, you will want to set this below the resulting TPS, so that the idle control can raise it to meet the idle, and close the throttle more if needed due to less load, etc.

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