Hi!
I'm having a few issues with the setup of the idle controller of a maxxEcu and am looking for someone who has experience and can help.
Some background information: the engine is a 2.5-litre type 4 running OEM-style intake and exhaust. The ignition is controlled by the maxxEcu, but is based on a modified dizzy and a stock coil. Unfortunately I'm not the builder of the engine, it's not even mine - it's owned by a friend of mine who I'm trying to help with configuring the efi. The ECU was programmed by a professional tuner, but it seems he didn't care or pay enough attention to things like warm-up or idle control...
The issue: the engine runs perfectly smooth, except for one rather annoying situation. Imagine rolling towards a junction without throttle at about 1300-1600 rpm and then depressing the clutch. The idle controller is unable to "catch" the change and the engine stalls. If the throttle is pressed ever so slightly before engaging the clutch (or at higher rpms), the engine runs smoothly.
Maybe someone has an idea, what can be changed. Of course I can fiddle around with the idle speed controller settings until it works, but I don't want to do that. I would like to understand the concept behind the controller (my personal goal with the whole thing, since it's not my engine...) and set it correctly.
Regards,
mike
Help with idle controller setup of a maxxEcu needed
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Hans_Sausage
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Bruce.m
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Re: Help with idle controller setup of a maxxEcu needed
What is the idle air valve set up?
Could be a simple on/off air valve, a PWM controlled valve or a stepper motor valve. Or none at all.
If the idle air comtrol is a bit slow to reqct for some reason , you can do the usual trick of adding an extra rpm line in the spark advance table at 600 rpm and set it to 15 degrees advance. When the engine dips below idle the advance increases, raising torque and acting as a cushion to prevent stall.
That might be the simplest method before you dive into the isle control and idle tuning which can be complex
Could be a simple on/off air valve, a PWM controlled valve or a stepper motor valve. Or none at all.
If the idle air comtrol is a bit slow to reqct for some reason , you can do the usual trick of adding an extra rpm line in the spark advance table at 600 rpm and set it to 15 degrees advance. When the engine dips below idle the advance increases, raising torque and acting as a cushion to prevent stall.
That might be the simplest method before you dive into the isle control and idle tuning which can be complex
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Paul H
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Re: Help with idle controller setup of a maxxEcu needed
Generally speaking it takes about 30 minutes to tune the main fuel and spark settings on a decent rolling road with a decent ECU that can be tuned in real time and then about 30 days on and off to perfect the map with warm up,idle low speed cruise etc. The rolling road tuner could probably do this but at at least £100 per hour the bill would be large and you don't use a rolling road to set up anything but medium to high load everything else is best done on the road with a datalogger. Use a decent stepper motor idle valve with decent flow capability and on a side note get rid of that modified dissy and stock coil
Real parts=Real Performance-Get Real
Opinion is the medium between knowledge and ignorance (Plato).
Opinion is the medium between knowledge and ignorance (Plato).
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Bruce.m
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Re: Help with idle controller setup of a maxxEcu needed
Paul, do you have a typical generic idle valve of choice? (Youve been a good source of suggestions in the past, for value-for-money parts 
)
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Hans_Sausage
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Re: Help with idle controller setup of a maxxEcu needed
Hi Bruce,
dunno why, but my response is waiting to be approved by the moderator... Could it be because of citations?
I don't want to copy everything I wrote there, but the engine uses a PWM-controlled idle air valve from a "baby" Benz 190 E.
Regards,
m.
dunno why, but my response is waiting to be approved by the moderator... Could it be because of citations?
I don't want to copy everything I wrote there, but the engine uses a PWM-controlled idle air valve from a "baby" Benz 190 E.
Regards,
m.
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Hans_Sausage
- Posts: 5
- Joined: Thu Apr 24, 2025 2:09 pm
Re: Help with idle controller setup of a maxxEcu needed
Hi,
I've decided to repost my reply as the moderator still hasn't approved my previous reply.
So the engine has a PWM-controlled idle air valve from a "baby" Benz 190 E. At a duty cycle of about 30 % it's closed, from 55% the engine speed goes over 1400 rpm and starts to oscillate (even if the ignition timing is fixed at 10° BTDC). We have adjusted the throttle body gap so that a fully heated-up engine runs at about 850 rpm when the IAV is closed.
I have added an extra column in the ignition table for lower rpm, but my understanding is that it only works when the idle controller is deactivated. If the idle controller is enabled (when the rpm falls below a certain value (700 rpm + rpm target) and the TPS is below 0.9%), then the ignition is set to change between 2° and 25° (the values can be adjusted) and the rate of change is controlled by the PID settings. There is also a ramp down time that defines the time how fast the ignition angle is reduced from the table value to the controller value when the idle controller takes over (now set to 2 sec). Let's look at the example of rolling up to a junction with no throttle and look at the rpm, idle target rpm and ignition angle logs: at 1800 rpm the idle target rpm is 900 rpm and the ignition angle is set in the ignition table to about 18° BTDC; at 1600 rpm the idle controller is activated - one gets a triangle bump of the idle target rpm value - it rises to 1600 rpm and then ramps down for 2 sec to 900 rpm again, but now the ignition angle changes from about 18° to the minimal set value of the controller, which is 2°. When the clutch is engaged, for example at 1300 rpm, the ignition angle rises to almost 22-23°, but this is not enough to prevent the engine from stalling. I have tried to increase the opening of the idle air valve, so that it's not fully closed when the engine is hot and the idle controller is activated - changing it from 30% to 38% somewhat solved the issue, but the engine is running with almost 1100 rpm then. The problem with this is that the idle valve remains open during "normal" idling, thus increasing the engine speed and resulting in the controller not reaching the set rpm target of 900 rpm.
My next idea is to take a closer look at the interaction between the idle controller and the fuel cut. Now the fuel cut is deactivated at 1250 rpm. When the clutch is engaged at 1300 rpm, the controller rises the ignition angle, but perhaps the engine is not getting fuel fast enough? If this doesn't work, the maxxEcu offers a second controller (PI only) for the idle air valve, which is intended to handle such cases - if the rpm target cannot be achieved with the ignition advance, the slower IAV is used for adjustment. So far, however, I have not been able to get this controller to work...
I completely agree, that a proper tune takes time. That's why I'm trying to help my colleague with the configuration. I would also love to get rid of the dizzy, but as I wrote at the beginning it's not my engine, and I suspect it has also something to do with the registration as a classic car. Unfortunately, in some parts of the world one have to take such things into account...
Regards,
mike
I've decided to repost my reply as the moderator still hasn't approved my previous reply.
So the engine has a PWM-controlled idle air valve from a "baby" Benz 190 E. At a duty cycle of about 30 % it's closed, from 55% the engine speed goes over 1400 rpm and starts to oscillate (even if the ignition timing is fixed at 10° BTDC). We have adjusted the throttle body gap so that a fully heated-up engine runs at about 850 rpm when the IAV is closed.
I have added an extra column in the ignition table for lower rpm, but my understanding is that it only works when the idle controller is deactivated. If the idle controller is enabled (when the rpm falls below a certain value (700 rpm + rpm target) and the TPS is below 0.9%), then the ignition is set to change between 2° and 25° (the values can be adjusted) and the rate of change is controlled by the PID settings. There is also a ramp down time that defines the time how fast the ignition angle is reduced from the table value to the controller value when the idle controller takes over (now set to 2 sec). Let's look at the example of rolling up to a junction with no throttle and look at the rpm, idle target rpm and ignition angle logs: at 1800 rpm the idle target rpm is 900 rpm and the ignition angle is set in the ignition table to about 18° BTDC; at 1600 rpm the idle controller is activated - one gets a triangle bump of the idle target rpm value - it rises to 1600 rpm and then ramps down for 2 sec to 900 rpm again, but now the ignition angle changes from about 18° to the minimal set value of the controller, which is 2°. When the clutch is engaged, for example at 1300 rpm, the ignition angle rises to almost 22-23°, but this is not enough to prevent the engine from stalling. I have tried to increase the opening of the idle air valve, so that it's not fully closed when the engine is hot and the idle controller is activated - changing it from 30% to 38% somewhat solved the issue, but the engine is running with almost 1100 rpm then. The problem with this is that the idle valve remains open during "normal" idling, thus increasing the engine speed and resulting in the controller not reaching the set rpm target of 900 rpm.
My next idea is to take a closer look at the interaction between the idle controller and the fuel cut. Now the fuel cut is deactivated at 1250 rpm. When the clutch is engaged at 1300 rpm, the controller rises the ignition angle, but perhaps the engine is not getting fuel fast enough? If this doesn't work, the maxxEcu offers a second controller (PI only) for the idle air valve, which is intended to handle such cases - if the rpm target cannot be achieved with the ignition advance, the slower IAV is used for adjustment. So far, however, I have not been able to get this controller to work...
I completely agree, that a proper tune takes time. That's why I'm trying to help my colleague with the configuration. I would also love to get rid of the dizzy, but as I wrote at the beginning it's not my engine, and I suspect it has also something to do with the registration as a classic car. Unfortunately, in some parts of the world one have to take such things into account...
Regards,
mike
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Bruce.m
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Re: Help with idle controller setup of a maxxEcu needed
Using idle controller to manage the ignition advance will be more complex. Not dealt with that myself.
Personally i try disabling that functionality (leaving the idle control handling the air valve) and see if you can get a stable idle without. Just save the tune beforehand so you can revert back if it doesn’t work
Personally i try disabling that functionality (leaving the idle control handling the air valve) and see if you can get a stable idle without. Just save the tune beforehand so you can revert back if it doesn’t work
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Hans_Sausage
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Re: Help with idle controller setup of a maxxEcu needed
This is the control strategy of the maxxEcu - it primarly uses the ignition to control the idle. I don't think it is possible to control the idle only with the IAV. It works in open loop as a temperature-dependent table, but these are simply fixed values. Then, of course, I can also set a fixed ignition angle for the idle, but I don't think it is possible to adjust the IAV duty cycle as a function of rpm...
Regards,
mike
Regards,
mike
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Bruce.m
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- Joined: Sun Aug 11, 2013 1:44 pm
Re: Help with idle controller setup of a maxxEcu needed
I had a brief look at the online maxecu manual. Under Idle ignition control it did suggest there was an option to “disable”?
https://www.maxxecu.com/webhelp/settin ... ntrol.html
But I didn’t read that deeply so may have misunderstood
https://www.maxxecu.com/webhelp/settin ... ntrol.html
But I didn’t read that deeply so may have misunderstood
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Hans_Sausage
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Re: Help with idle controller setup of a maxxEcu needed
Yeah, you're right.
I have to check, but I think the IAV is not activated at all when the idle controller is disabled. The ignition values will then be taken from the ignition table - your suggestion with an additional column for 600 rpm would come into play... The next test session is scheduled for Friday, so I will try to explore all possible options.
Regards,
m.
I have to check, but I think the IAV is not activated at all when the idle controller is disabled. The ignition values will then be taken from the ignition table - your suggestion with an additional column for 600 rpm would come into play... The next test session is scheduled for Friday, so I will try to explore all possible options.
Regards,
m.