Setting up ignition based idle control
Posted: Thu Jul 04, 2019 8:05 am
This may well be obvious to many on here, but it wasn't to me until I thought about it!
My idle control timing limit parameters were set at +25 degrees down to -15 degrees. The way the system works is to reduce timing if idle speed is too high, and increase it when too low. Timing at idle was originally set up at 10 degrees (on the main ignition map).
My particular requirement is to have decent control over idle in my automatic - in other words, so the idle control copes with the load on the engine when Drive is engaged. However similar issues may arise on a manual car with aircon and cooling fan loads at idle.
My car idled very poorly in general - lumpy, variable, and sometimes stalling. As suggested in the manual, I went in to reduce the ignition timing at idle in order to give the idle controller sufficient scope to increase timing to compensate for load, so I reduced it to 6 degrees which gave a steady idle speed (with idle control turned off) of 1200rpm vs the 1300+rpm I was seeing at the original setting of 10 degrees. Then I switched idle control back on and monitored the adjustments in timing being made by the ECU to control idle both in gear and in neutral. In gear, timing was being advanced to 15 degrees with relatively poor running, and in neutral it was very lumpy and variable with the timing dropping below -5 degrees. I then disabled idle control again and played about with ignition map settings to find out the effect of timing on idle speed. It turned out that idle speed started to reduce when the timing was increased above 10 degrees, with 10 degrees giving the maximum speed. Reducing timing, idle behaviour became erratic and lumpy when timing dropped below -5 degrees. There was therefore no point allowing the system to set timing outside these limits! Once these were set in the system, idle behaviour was transformed.
So, if you are using timing control of idle, my advice is to test idle behaviour first with different timing settings to find out the optimal maximum and minimum settings for your engine, and use these.
I don't think I now need an idle air control valve.
My idle control timing limit parameters were set at +25 degrees down to -15 degrees. The way the system works is to reduce timing if idle speed is too high, and increase it when too low. Timing at idle was originally set up at 10 degrees (on the main ignition map).
My particular requirement is to have decent control over idle in my automatic - in other words, so the idle control copes with the load on the engine when Drive is engaged. However similar issues may arise on a manual car with aircon and cooling fan loads at idle.
My car idled very poorly in general - lumpy, variable, and sometimes stalling. As suggested in the manual, I went in to reduce the ignition timing at idle in order to give the idle controller sufficient scope to increase timing to compensate for load, so I reduced it to 6 degrees which gave a steady idle speed (with idle control turned off) of 1200rpm vs the 1300+rpm I was seeing at the original setting of 10 degrees. Then I switched idle control back on and monitored the adjustments in timing being made by the ECU to control idle both in gear and in neutral. In gear, timing was being advanced to 15 degrees with relatively poor running, and in neutral it was very lumpy and variable with the timing dropping below -5 degrees. I then disabled idle control again and played about with ignition map settings to find out the effect of timing on idle speed. It turned out that idle speed started to reduce when the timing was increased above 10 degrees, with 10 degrees giving the maximum speed. Reducing timing, idle behaviour became erratic and lumpy when timing dropped below -5 degrees. There was therefore no point allowing the system to set timing outside these limits! Once these were set in the system, idle behaviour was transformed.
So, if you are using timing control of idle, my advice is to test idle behaviour first with different timing settings to find out the optimal maximum and minimum settings for your engine, and use these.
I don't think I now need an idle air control valve.