[s13 @ fullboost]

You can play with the IACV adjustment located on the back of the intake, I believe counter clock wise will raise RPM & clock wise should lower.

Originally Posted by Kingtal0n

The diagnostic moral here is that airflow sets the idle speed, the system should be pressure tested, make sure it is air tight i.e. you should be able to shut an engine off by covering the throttle body and similar ports (with your hand for example if you cover the TB/IACV the engine should die, if it kept running you have a leak somewhere)

fuel and timing influence/adjust idle speed, while airflow always sets the idle speed

How to adjust the idle speed on a high performance engine for maximum compliancy (very unlikely to suffer bearing damage due to low idle speeds, which may occur on engines with older ECU or old technology IACV type valves)
1. Get the engine warm, set idle Air fuel ratio, use 15* btdc on sr20det engines with a MAF sensor for best results, allow idle wander up to 22* btdc
2. Load the engine with headlights and electric fans, and any other devices you intend to run in the car frequently.
3. disable the IACV somehow; plug airflow holes that lead through any automatic idle control valves so no computer idle speed adjustments can occur for the next step
4. Engine warm and loaded up, set your idle speed using IACV manual adjustment (or throttle body base adjustment if the engine in question has no IACV) 10-60rpm below desired Idle speed.

5. Plug back in (re-enable) the IACV (or computer control) so the computer can use the valve to add that 10-60rpm back into the idle speed to achieve desired idle speed. If the ecu is OEM this is around 850rpm on sr20det. otherwise, units like the PFC have adjustable desired idle speed. If my desired idle speed is 900rpm for example, then my base idle speed with no computer control would be around 860rpm so the computer only needs to add a little bit of air to reach 900. Keeping the two settings (base idle and desired idle) very close will help stabilize the idle of the engine, especially if it has a long duration camshaft.