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DTC codes / Chrysler codes / P1299

P1299 · ChryslerVacuum Leak Found (IAC Fully Seated)

P1299 on Chrysler vehicles means the powertrain control module (PCM) commanded the idle air control (IAC) valve to fully seat and then measured an unexpected drop in manifold vacuum, confirming a vacuum leak. The PCM detects this by monitoring the intake vacuum through the manifold absolute pressure (MAP) sensor while the IAC is driven closed, and it sets the code when the vacuum reading does not rise as expected.

SystemPowertrain
Code typeChrysler specific
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering (injector circuits)

Symptoms you may notice

  • Check engine light illuminated, often with no other noticeable symptoms
  • Rough or fluctuating idle, sometimes stalling when coming to a stop
  • Hissing or whistling noise from the engine bay at idle
  • Higher than normal idle speed that does not settle after the engine warms up
  • Poor fuel economy or a rich-running condition noticed over time

Common causes, most likely first

  1. Cracked or disconnected vacuum hose, especially at the intake manifold or brake booster
  2. Leaking intake manifold gasket or throttle body gasket
  3. Faulty or stuck-open positive crankcase ventilation (PCV) valve or hose
  4. Leaking brake booster diaphragm or check valve
  5. Damaged or misadjusted idle air control (IAC) valve or its wiring
  6. Cracked intake manifold or vacuum reservoir
  7. Loose or missing oil dipstick or oil filler cap allowing unmetered air

How to diagnose and fix it

  1. Inspect all vacuum hoses and connections for cracks, splits, or disconnections, starting at the intake manifold and brake booster
  2. Check the PCV valve and hose for proper operation and sealing
  3. Perform a smoke test on the intake system to locate leaks that are not visible
  4. Verify the IAC valve is clean and moves freely, and that its connector and wiring are intact
  5. Test the brake booster for a ruptured diaphragm by checking for a hard pedal and vacuum loss
  6. Inspect intake manifold gaskets and throttle body gasket for leaks, replacing as needed
  7. Clear the code and verify the repair by confirming fuel trims and idle vacuum return to normal

Hidden vacuum leaks that trigger P1299

  • A leaking brake booster diaphragm can cause this code without any brake pedal symptoms, so always test the booster with a vacuum gauge.
  • The oil dipstick and oil filler cap are often overlooked; a missing dipstick allows unmetered air into the crankcase and sets P1299.
  • A dirty or sticking IAC valve can mimic a vacuum leak by not seating fully, so clean or test the valve before replacing expensive gaskets.
  • Intake manifold gasket leaks on Chrysler engines often occur at the lower intake runners and are invisible without a smoke machine.
  • This code can be set by a faulty MAP sensor that reports incorrect vacuum, so compare its reading with a mechanical vacuum gauge.

Can I keep driving with P1299?

You can usually drive the vehicle short distances to a repair shop, but avoid prolonged idling, heavy loads, and aggressive acceleration because a vacuum leak can cause stalling and poor fuel control. If the engine idles very rough or stalls frequently, stop driving and have it towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Chrysler vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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