MoTeC Global Forum

Got 2006 STi DBW with M800 ECU, the car runs really great and it makes a good power, but the only thing that i cant get right is the idle. i cant get the engine idling smooth with hunting; if it idle good when the engine is warm, it will hunt when its cold and visa verse. during decl it will hunt for a few seconds till it satel smoothy.

Tried changing the PI, but as i sated above i cant really make it stable when cold and warm.
it seems that the PID setting im using are wrong somehow .

Its my first time doing DBW car. ive always thought the DBW are easier to get to idle smoothly .


Thanks.
Majed.

You need to have the Normal position and maybe the idle aim rpm increasing with lowering engine temp to fix the startup idle hunting. Have you tried increasing the Derivative to stop the hunting?

Read this Motec sheet

Ive tried a few different strategy tuning the normal position table, now its set with aim idle and coolant temp, and it seems respond much better, the hunting is not completely gone though.

It behave little bit wired, if it idles nice and smooth w/o AC, but as soon as i switch the AC on, it start hunting for a few secounds then it settle down, blip the throttle and it stalls and the engine dies.
If ituned it with the AC on it will be nice and smooth, switch the AC off and it keep huning.

I tried increasing the derivative but it make the problem worse.

Thanks for the sheet, know i have alittle more grasp on the PID system, will give it another try tomorrow when the engine is dead cold.

Regards.
Majed.

3000HP wrote:Ive tried a few different strategy tuning the normal position table, now its set with aim idle and coolant temp, and it seems respond much better, the hunting is not completely gone though.

It behave little bit wired, if it idles nice and smooth w/o AC, but as soon as i switch the AC on, it start hunting for a few secounds then it settle down, blip the throttle and it stalls and the engine dies.
If ituned it with the AC on it will be nice and smooth, switch the AC off and it keep huning.

I tried increasing the derivative but it make the problem worse.

Thanks for the sheet, know i have alittle more grasp on the PID system, will give it another try tomorrow when the engine is dead cold.

Regards.
Majed.

1) Do you have many cells around your idle point?

2) Does the ECU know when the AC is on? (...LTR or GED...)

You MUST understand how the throttle position affects the RPM, do this as a test with the idle control switched off using the translation table. For each increment of throttle position you want an equal increase in RPM..........FUEL AND IGNITION TABLE SHAPE AND ACCURACEY OF YOUR TUNE WILL GREATLY AFFECT THIS. People forget that it is fuel air and spark.

Lowering the ignition timing can dull down the engines response to throttle and will mean that for the same P gain you will have less sensitivety. Injectors and cams will also greatly affect idle.