idle speed and vacuum during warmup

[Yves]

When warm the engine idles at 69 -70 kPa with 19° advance and 1000 rpm. So far it seems like 19° provides the best compromise between a stable AFR at idle and rpm. Camshaft has 247/249 at 0.05 with 106 LCA so a lot of overlap. Engine runs on itb's.

I was working with the idle stepper and to some extent it seems to work, except when really cold, when the added air doesn't seem to help anything. During cold startup she seems to drop rpm's to below 800 (first column in my rpm is 800 second is 1000). I've noticed that during these low rpm cold conditions that she runs in the 80+ kPa zones, which have a substantial higher VE value of around 45, whereas warm idle has 32. This makes the engine run really rich during those cold moments. Not sure if that has the effect of keeping the rpm down, although the stepper is adding air to it.

I was thinking about pulling the numbers in that +75 kPa and 800 rpm area lower, but sometimes during pulling away with small throttle opening it seems to end up in that area as well, so that might be a wrong move to do.

What's the solution here ? More ignition timing in that area ?

[Matt Cramer]

More ignition timing doesn't sound like a bad idea, although consider using Cold Advance rather than tuning the table. Remember your goal at idle tuning is to get the power the engine is putting out to balance out the frictional losses. If it's idling too slow, you will want to either add more air (which apparently isn't working) or tweak the ignition timing to increase power at that specific point.

[Yves]

I tried giving it 4° more when cold, but it only marginally improves rpm with about 100 rpm. Still a 150 rpm below target.

[kaeman]

Hey Yves, How are you hooking up the idle stepper motor to your manifold, I know that the 80 kpa reading is probably due to the hookup of your stepper motor into your vacuum ports from the itb's this would make a huge vacuum leak as seen by the map sensor. I am not using any idle air controls on my engine because the warm up enrichment and cold start settings make it easy to start even when cold here. I would guess that if you plugged the vacuum line to the stepper motor and then retuned your warm up you wouldn't have to much trouble... I know that our itb's create lots of different behavior in tuning and driving. I know my engine starts easily at any temp from 38 to 105... and I don't use any kind of air valve.
Good luck.

[Yves]

Hi Kae,

The stepper is connected to the airbox where it takes it's air (clean air source) and then it goes to the vacuum chamber underneath the runners. The runners all have small holes (about 1/4") that connects them to the vacuum chamber. The map is also connected to this common plenum.

The thing is that the engine can run on 700 rpm, but it doesn't really like it and running is pretty uneven. The technologie to improve upon that low rpm is there so why not use it.

The strange thing is that it doesn't seem to use the additional airflow. I thought it had to do with the fueling but that doesn't seem to be it either. Not sure what's going on.

Maybe something in the hysteresis setting of the idle control.

[Yves]

I found the issue : the idle cold taper time was set to 40 seconds and the steps during that time to 120...