TIMING at idle.

[LS1toSVT]

Using your predator, where does your timing hover around at idle?

Mine is in the 20's. As in low 20's and then will hit 29 and then jump back down. Its very random.

 

[eficalibrator]

Timing is intentionally retarded a bit at idle to control torque.

The whole point of idle control is to maintain zero net torque output at the flywheel. Any positive torque, and the engine accelerates. Any negative torque and it slows down. Maintaining zero torque net gives a steady idle speed.

The trick is that when loads change (friction, airflow, A/C usage, alternator duty cycle, etc...) the EEC must respond very quickly to avoid stalling or surging. There are two ways to control this, a slow one (IAC flow) and a fast one (spark advance). The EEC uses varying amounts of spark to instantaneously change engine torque and control idle speed. As such, you will sometimes see what look like large swings in delivered timing at idle as loads change along with IAC position to maintain a steady idle.