Idle Tuning - Speed Density vs. Alpha-N

**SSSTANG** · 06-25-2016, 09:33 PM

I've been using Alpha-N for almost a year, because I couldn't get a consistent idle using Speed Density. Engine idles between 60 & 65 kPa. I've been satisfied, it idles. I read this on YellowBullet: http://www.yellowbullet.com/forum/sh....php?t=1852514, and it got me thinking. Today I changed to Speed Density, and it would not idle. I didn't adjust the throttle body idle screw. If it idles fine in Alpha-N, would it be normal to have to adjust the idle screw just because I switched to Speed Density?

**S2H** · 06-25-2016, 10:42 PM

It's likely a fueling issue. When you switch from Alpha-N to Speed Density, your cells in the Base Fuel Table where it idles will be VERY different.
Alpha-N, Idle is always the lower left corner of the table.
Speed Density, it's going to be somewhere else, guaranteed.
You'll need to do almost a complete retune of the Base Fuel Table, after switching from Alpha-N to Speed Density.

**SSSTANG** · 06-26-2016, 01:42 PM

OK, I bumped the idle via the idle screw, set Learn to 100% above 800 RPM, Closed Loop & Learn Compensation to 100%, and switched to speed density. It was idling at 1200 rpm, and came down as I was adjusting the idle screw until 1000 rpm. Anything below 1000 rpm and it stumbles & dies without the IAC catching it. As it begins to stumble, I can see the IAC fluctuate, but it's too late to control the idle speed. P Term 50, D Term 70.