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Cold Idle

A raised idle target while the engine is cold, falling toward normal idle as coolant warms up.

Demo build: this panel is locked

The cold-idle card is available in the full game. See Demo vs Full Version.

What it is

A cold engine is mechanically reluctant: oil is thick, fuel vaporizes poorly, and friction is high. Cold idle (fast idle) raises the target idle RPM while the engine is cold, then lowers it toward the normal target as coolant warms.

It is an offset added to your base idle target. The default offset:

Coolant (°C) −40 −20 0 20 40 60 80 and above
Offset (RPM) +1150 +950 +550 +250 +100 +50 0

With an 850 RPM base target that gives 2000 RPM at −40 °C, 1800 at −20 °C, 1400 at 0 °C, 1100 at 20 °C and 850 at 80 °C.

The cam floor. The idle target can never go below the lowest speed the fitted cam can hold stable — about 800 RPM plus 7.5 RPM per degree of overlap above 20°, clamped to 700–1600 RPM. A big cam therefore raises your idle instead of making it hunt.

This is a target for the idle control system, which holds it by adjusting the throttle blade — it isn't extra fuel (that's warmup enrichment).

Why it matters

  • A higher idle gives the cold engine the airflow and energy it needs to avoid stalling when it's most fragile.
  • The extra RPM and load speed up warmup, getting the engine to operating temperature (and out of enrichment) sooner.

If cold idle is set too low, a cold engine stalls at rest; too high, and it races uncomfortably and warms slowly to the right RPM.

How to tune it

Shape the offset curve against coolant temperature: high at the cold end, smoothly reaching zero at operating temperature. Pair it with warmup enrichment so the cold engine has both the air (idle target) and the fuel it needs.

Rule of thumb

Set the cold target just high enough to idle rock-steady without throttle input from cold — higher than that only wastes fuel and noise.

In the game

IGNITION page → right column → COLD IDLE TARGET (the top card). It shows ECT: … and Offset: +N → M RPM. Watch idle RPM step down as the COOLANT bar climbs toward operating temperature.