MaxxECU Idle Control and Off Idle Surgin

Hello,

I have an LS3 swapped e82 BMW running Maxx Race. Im running TBW, BTR stg 4 cam, otherwise pretty normal setup.

I'm having a few issues.

1.) Idle - I cannot get it to idle smoothly without oscillation. Maxx uses a PID loop and I've spent hours adjusting parameters without finding one that works. Its close, but still oscillates. How do I determine the correct PID settings? I've tried both air OR timing as well as air AND timing control strategies.

2.) When idle control kicks in (I have this set at 1500rpm) the car starts to buck wildly. I have idle control set to turn off with 1.5% throttle input - and my throttle inputs are rock solid - no oscillation.

PID loops for DBW control is great with throttle body tracking throttle pedal with no oscillation or weird behavior. Has anyone else experienced this with Maxx? I'd be happy to upload my tune file but the forum here says the file type is NULL and will not allow an upload

TIA

YWIA,

You need to put on your diagnostics hat a little bit here. A lot is happening during idle and oscillations can come from many different places. DBW position inaccuracies, DBW movement, Fueling, Ignition timing, as well as influence from the feedback from idle control settings just to name a few.

As it does all of these oscillations, confirm what is steady and what is moving. If the actual TPS is a solid number, meaning no DBW movement, you can eliminate throttle influence. You can now focus on MAP, Fueling and ignition timing. If the TPS is fluctuating, identify the DBW target value. Confirm whether the ECU is requesting the DBW movement or if the DBW cannot hold a steady position.

Many other things will change with TPS movement and can give false identifiers as to what needs to be corrected. Ideally you have a TPS based fuel table. This makes it easier to lock down the VE in the idle region and prevent the ECU from making overly aggressive fueling changes due to small oscillations in MAP. Ignition at idle should be very steady as well. Start here and let's see what you can identify.

EB Turbo: In order to reduce the number of variables, I've opted to tune in timing only mode. I believe this removes throttle body movement. I am using a MAP based VE table which may be the source of my headaches as I've read that cams with a lot of overlap can have difficulty with MAP fluctuations due to the low vacuum at idle (or high pressure, in absolute terms). My timing is pretty steady, but I have not disabled fuel adaptations at idle. I may try to figure out how to lock that to remove that variable as well.

How do I address the instant surging that takes place as soon as idle control kicks in? Thank you for your response.

Assuming the throttle isnt moving and confirming are different things. Just because the ECU is told not to do idle control with the throttle body, doesnt mean the throttle body is at a steady position. When tuning and diagnosing these issues, you should confirm as much information as possible. Also changing to a TPS based fuel table isnt necessary because you have a big cam. NA, ITB, CAM size, Turbo, Supercharged, all of them work well with a TPS based fuel table.

If there is still surging when idle control is turned on, you will still need to confirm what is actually happening. If the idle is 1000 rpm and the target is 800 rpm, there is no control over DBW position so the ECU will add/remove timing or add/remove fuel. If these are set too aggressively and it is not possible to reach the target idle speed, things might get out of hand.

You need to confirm what you have and don't have. The ECU will have table values and final values. If you have a base idle target of 800 rpm, a coolant temp offset of 400 rpm, and an AC idle kick of 250 rpm, your idle target may be 1450 rpm. Just looking at the base idle table and seeing 800rpm isnt the actual idle target. Now this may not be your situation, but this goes for almost every other control function in the ECU. You should confirm what the TPS target is and compare to actual, you should see when idle control is turned on that you get reasonable values. Same for fueling, ignition timing, Idle speed targets...