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Reply to "Fuel Injection and Electronic Ignition for VW engines - Speeduino Style"

@edsnova posted:

Right now my off-throttle (high MAP) ignition timing numbers at idle are much, much lower: my "trough" is at 800 rpm at maybe 8 degrees (I'd have to hook up the computer to check the table). I'd thought the trough should only be a degree or two. You're saying it can be more pronounced?

I did some testing this morning on the question you raised about how many degrees of advance the "trough" should be to help hold the idle steady. I made a test tune that disabled all idle air addition and idle advance.

At 8 degrees advance, hot idle settled in around 800 RPM.  Setting the bin below 800 RPM at 8 - 15 degrees didn't make a whole lot of difference in idle or idle recovery. Setting the bin below to 0 degrees advance reduced idle RPM and idle recovery.

The distance between the idle and the bin below made a difference, too. If I moved the bin below to 700 RPM, any changes up or down were much more pronounced in the impact on idle speed and recovery. Setting the bin below idle to 600 RPM (200 below) reduced the sensitivity of the settings (I'd recommend setting the bin below at least 200 RPMs away from idle speed).

Finally, I tested what optimal timing my engine liked at 800 RPM. 35 degrees advance seemed like the point at which idle volumetric efficiency was met (MAP readings didn't go any lower above 35 degrees at 800 RPM).  That means if you wanted to add timing around the idle trough to stabilize it when you come off of the throttle, you could make the bin below idle up to 35 degrees. In practice, when I played around with it, 2 to 5 degrees above idle speed advance seemed to work just fine.

Let me know if you have any questions,

Mike

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