Which helps more against cam surge: adding timing in the low-RPM spark tables, raising minimum idle airflow, or dialing in the VE and MAF tables?
Dialing in VE/MAF fueling plus a proper idle spark window beats raising minimum idle airflow on its own: fueling first, spark second, airflow last. Raising minimum airflow alone mostly masks a bad tune — and a rich idle is itself a common cause of surge.
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Who this applies to
- Computers: P01, P59, E38, E67
- Engines: LS1, LS2, LS3, LS6, LS7, LM7, LQ4, LQ9, LY6, L96
- Transmissions: 4L60E, 4L80E, 6L80E, T56, TR6060
- Not for: Gen V E92 LT engines (different idle torque model)
P01/P59 (Gen III, cable or electronic throttle)
- Disable adaptive idle spark, then find the best base spark at target idle RPM by minimum MAP; restore a linear adapt window of -5° overspeed / +5° underspeed.
- Tune the idle-region VE table (at and below idle RPM) in open loop with a wideband; do not run a rich idle, and expect big cams to corrupt both wideband and narrowband readings down low. open loop, tune to minimum MAP
- Straighten the idle over/underspeed spark correction tables into a linear, monotonic taper — a table that quits pushing advance and drops to 0° at extreme underspeed is inherently bistable and self-sustains oscillation.
- Set base running airflow so the throttle body holds near-steady at idle; if the TB stays steady while it surges, the airflow is close and the problem is timing and fuel. warm RAF ~13.9 g/s resolved a documented surge case
E38/E67 (Gen IV, drive-by-wire)
- Engine > Idle > Airflow: set base idle airflow per gear and P/N; start near stock and raise in 1-2 g/s steps, watching STIT/LTIT.
- Engine > Spark > Advance: set idle base spark with a real adaptive over/underspeed window below it — maxing out base spark leaves the adapt nothing to work with. leave an adapt window
Careful
- If fueling and spark are in range and the TB stays steady but it still hunts, look mechanical: vacuum leak, exhaust leak ahead of the O2 sensors, or a lightweight flywheel needing PID work — stop changing tables and log instead.
- Big cams corrupt wideband and narrowband readings at idle; verify with minimum MAP at target RPM, not just the gauge.
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Check this first
- Log RPM, spark advance, STIT/LTIT, and IAC counts (or ETC position) through a throttle stab and drop-to-idle; capture the settle curve and look for critically-damped vs oscillating response.
- Check the over/underspeed spark tables for non-monotonic dips — a curve that drops to 0° at extreme underspeed is inherently bistable and sustains oscillation by itself.
Try this, then this
- Disable adaptive idle spark and find the minimum-MAP spark point at target idle; then restore a -5°/+5° adapt window. — Adaptive spark hides how bad fueling and base spark really are; tuning around it leaves the oscillation in place. Worked if: MAP reads minimum and holds steady with adapt disabled.
- Fix the idle mixture at and below the idle RPM range; bias indicated-lean if overlap looks like it's corrupting the O2 readings. — Rich idle is a direct cause of surging, and big cams corrupt both wideband and narrowband readings at idle. Worked if: MAP drops at the same idle RPM.
- Straighten the over/underspeed spark tables into a linear taper. — Non-monotonic spark curves are bistable — stepping into the dip once starts an unending oscillation. Worked if: No repeated hunting after a rev.
How you know it's fixed
- Throttle position stays near-steady at idle while RPM holds target.
- Idle fueling shows minimum MAP at target RPM with trims near zero.
Key numbers
| What | Value |
|---|---|
| Priority order for taming surge | 1) idle mix, 2) idle spark, 3) airflow PID |
| Idle spark adaptive window | -5° overspeed / +5° underspeed, linear taper |
| Warm base running airflow that resolved a documented surge case | 13.9 g/s |
Time and cost: Tuning time only: a few hours of logging and iteration with HP Tuners and a wideband; no parts required.
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