High Idle Issue

[Graham BPT]

Hey everyone - I work with a lot of Subarus on the G4X plug-in ECUs.  Most of the time, I can do a full APS and E-Throttle calibration and then have good and normal idle control where an idle position of 1-3% at full operating temp will idle the car nicely, right on target but from time to time, I have some cars that idle too high, say around 1000 to 1100 with a 900 rpm target even as the idle base position is allowed to go down to zero.  TPS will be 4.5-5% and won't come any lower so the idle stays high.

What I can seem to do to work around this is go into the TPS (Main) closed voltage and lower the voltage down and that will cause the ECU close the throttle more and bring idle down but this seems like a work around rather than the correct way to handle this.

So, I'm wondering if there's something I am missing or a better way to deal with this.

Is there something that limits the TPS position at idle?  I'm wondering why and idle base position of zero can't/doesn't result in a lower TPS opening to bring idle lower?

Thanks!

[Adamw]

It could be 20 different things.  Will need to see the log and tune.  

[Graham BPT]

On 1/14/2023 at 12:59 AM, Adamw said:

It could be 20 different things.  Will need to see the log and tune.  

Sure.  I'll work on getting same data to show what I mean.  

In the meantime, can you help me understand the relationship between idle duty percent and TPS on a drive by wire car?

If idle duty is reduced to zero, shouldn't that be closing the throttle to a point where the engine rpms come down to the point of nearly stalling the engine?

Is there a minimum TPS value hard-coded into DBW logic to prevent that perhaps?

[Adamw]

28 minutes ago, Graham BPT said:

can you help me understand the relationship between idle duty percent and TPS on a drive by wire car?

Im not sure what you mean by "idle duty percent".  Do you mean the idle position?  If the idle actuator is set to E-throttle, then the idle position is TPS% and this is added to the e-throttle target and offsets etc.

 

28 minutes ago, Graham BPT said:

If idle duty is reduced to zero, shouldn't that be closing the throttle to a point where the engine rpms come down to the point of nearly stalling the engine?

If you had 0% in your idle base position and 0% in your E-throttle target table and all actuator offsets where set to zero then the throttle would be sealed closed at 0% so the engine wouldnt run assuming air cant enter via some other route. 

But as I said before there is a long list of things that may prevent that from happening which is why we need a log.  It could be for example antilag or gearshift overrides, idle or throttle PID settings, interpolated throttle target tables, clamps, closed loop, all off the dashpot/PS/AC/startup offsets, it may not even be entering idle mode... 

 

28 minutes ago, Graham BPT said:

Is there a minimum TPS value hard-coded into DBW logic to prevent that perhaps?

Not hard coded, but there is a user set min and max clamp.