P0519 — Idle air control system not working properly

The engine's idle air control system is not performing as expected, causing irregular or unstable idling. This can happen when the system controlling airflow at idle is dirty, faulty, or has wiring issues. It usually triggers when the engine computer detects the idle speed is outside normal limits and tries to adjust it but fails.

Common causes

The cause is almost always one of a few things. Here they are — P0519 rarely comes from anything outside this list:

• Dirty or clogged idle air control valve
• Faulty idle air control valve
• Vacuum leaks near the intake manifold
• Wiring or connector problems in the idle control circuit
• Faulty engine control module (rare)

Where to start

In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:

1. Clean the idle air control valve and throttle body
2. Inspect and repair vacuum leaks
3. Check and repair wiring/connectors related to idle control
4. Replace the idle air control valve if faulty
5. Scan and test engine control module if needed

That is what holds for P0519 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.