Use timing to help idle, not fight it
Most engines idle somewhere between 500 and 1000 RPM. In that band, the idle control system is working to hold a target speed, and the ignition table can either help it or make its job harder.
The first rule is consistency. At idle loads, keep the timing across 500 to 1000 RPM the same or very close. If timing changes a lot from one RPM column to the next, every small RPM wobble changes torque as well, and the idle controller ends up chasing its own tail.
Make the engine self-correcting
The trick we use is to run slightly more advance at 500 RPM than at 1000 RPM in the idle load rows. Here is why it works:
- If RPM sags, the engine moves into cells with a bit more advance, makes a little more torque, and pulls itself back up.
- If RPM rises, it moves toward slightly less advance, and torque eases off.
The result is an engine that finds a stable balance point on its own, with the idle valve only doing fine adjustment. Keep the difference small. You want a gentle slope, not a cliff.
Get the idle fuel right first. A lean or rich idle hunts no matter what the timing does. See Tuning for Idle (fuel), then Idle Control Tuning.
Related: Tuning Base Tables and Idle Control.
