Stalling and Oscillation at Idle with AC On

[Ken Hill]

Idle control on my Plug-In G4X ECU in my 2002 FLNB MX-5 Is great when no accessories are on.  However, when a fan or AC turn on while idling, the engine speed falls and then oscillates before stabilizing.  In about 1 out of 3 times, coming to a stop the engine speed will dip and sometimes stall.  I have Quick Tuned the 700RPM to 2000RPM, low map area of my fuel table several times.  I believe the fuel in correct in that area, but when the oscillations start, the AFR varies between 10:1 and 16:1.  As far as I can tell, the AFR goes lean when the fan or AC energizes.

Attached are two logs.  "Stall" shows the engine stalling when rolling up to a stop.  "Oscillation" shows the engine speed oscillating with the AC turned on at idle.

I'm stumped on these two issues.  Any help would be greatly appreciated.

Stall 2023-09-3 4;17;29 pm.llgx Oscillation - 2023-09-3 4;20;58 pm.llgx Hill Link J.pclx

[essb00]

Stalling has more to do with the idle control trying to go to min clamp while you're on engine braking (no speed lockout).
Oscillation is because of both idle speed control settings and too early overrun fuel cut.

Overrun fuel cut activates too early - due to no activation delay.
Put ORFC Activation Delay 1.0s, Torque Reduction/Introduction Time 1.5s

Ide Speed Control
Speed Source Lockout - Driven Wheel Speed
Speed Lockout - 10 kph
APS/TPS Lockout - 0.5 %
RPM Lockout Above Target 500rpm

Integral Gain 0.3

Try those, then do another log, then upload including the updated tune file.

[Ken Hill]

Thank you for the suggested changes.  I have made them all, except for Integral Gain.  I do not have that parameter, only Proportional and Derivative.

 

[curly]

That's idle ignition control. I believe he's referring to the integral gain under idle actuator settings.

[essb00]

Here you go...

[Ken Hill]

Thank you Curly and essb.  I missed the Integral Gain setting in the Idle Speed Control Window.  With the suggested changes from above made in the attached K file, the idle is performing better.  Attached are the logs with details on each one below.

Coming to a Stop with AC 1:  The first stop logged.  The idle speed oscillated during Dashpot decay and hold and decay time.

Coming to a Stop with AC 2:  Made a few minutes later.  Only a single cycle of oscillation at a much lower frequency.  Again, during Dashpot hold and decay time.  I suspect the Dashpot settings need to be adjusted.  However, I made about 10 or so more stops in my neighborhood with little to no oscillations.

Idle Turn AC on and off: While idling cycling the AC on and off.  At both transitions, idle speed fell below target, but recovered.

Coming to a Stop with AC 1.llgx Coming to a Stop with AC 2.llgx Idle Turn AC on and Off.llgx Hill Link K.pclx

[essb00]

On "Coming to a Stop with AC 1", you've got the overrun fuel cut activating... You may need to reduce your dashpot percentage to maybe 2.5%.

On "Idle Turn AC on and Off", you need to increase the values of your idle base position table to have minimum values 32 on normal operating temps.

[Ken Hill]

The Dashpot and Idle Base Position changes did the trick.  I drove to and from work today with about 10 stops along each way.  In the morning I drove in with no AC to make sure the changes did not adversely effect the idle with no accessories.  The drove home in the afternoon had the AC on the entire way.  Twice out of 10 stops the idle speed oscillated 2 cycles and then calmed right down.   I think Dashpot and Speed Lockout may need a bit more change.  After raising the Idle Base Position, I had to lower the Startup and AC Offset Tables by the same amount to keep the idle speed the same when using these tables.

Thanks again for the guidance.

Ken