Air intakeGeneric OBD-II codeUrgency: Garage soon

P0505 on Hyundai: causes and affected engines

P0505 means: idle control system: malfunction.^[1][2][3] Hyundai has 6 documented faults that can trigger it, across 6 engines, including 1.6 GDI / T-GDI, 1.0 T-GDI, 1.1 and 1.4 CRDi and 2.0 / 2.4 GDI and T-GDI (Theta II). Only a diagnosis can confirm the cause on your car.

Documented faults

that can trigger it

Engines

used by Hyundai, with at least one of them

Hyundai models

with at least one of these faults

Urgency

Garage soon

Reviewed on 31 October 20263 sources How we work

Documented faults in Hyundai engines that can trigger P0505

Grouped by engine or model, from most to least important. These are faults with carbon build-up in the intake: not all of them will necessarily set the code, and only a diagnosis confirms the cause on your car.

1.6 GDI / T-GDI

In i20 III, i30 II, i30 III, i40, ix35, Kona I and 3 more models

- Medium severityFrequency: CommonIntakeCarbon build-up on the intake valvesBeing pure direct injection, with no port injectors to wash the valves, the 1.6 GDI and T-GDI build up intake carbon with mileage: unstable idle, jerking or loss of power. A design trait of all direct injection, not a manufacturing fault.

1.0 T-GDI

In Bayon, i20 II, i20 III, i30 III, Kona I and Kona II

- Medium severityFrequency: OccasionalIntakeCarbon build-up on the intake valves and coking of the injectorsThe direct injection on the 1.0 T-GDI does not wash the intake valves with fuel, so over the kilometres carbon builds up on them and on the injectors. It causes loss of power, jerking and higher fuel consumption; it is fixed by cleaning the manifold and valves, without damaging the engine.

1.1 and 1.4 CRDi

In i20 I, i20 II, i30 II and ix20

- Medium severityFrequency: OccasionalInjectionCarbon build-up on the common-rail injectorsThe common-rail injectors on the 1.1 and 1.4 CRDi accumulate carbon deposits with urban use and short trips, which can make cold starting harder and cause jerking; German buying guides cite it as typical wear, not as a design fault specific to the engine.

2.0 / 2.4 GDI and T-GDI (Theta II)

In i30 III, Kona I and Santa Fe III

- Medium severityFrequency: OccasionalIntakeCarbon build-up on the intake valves of direct-injection Theta II enginesAs with any direct injection, petrol does not wash over the intake valves and deposits build up. A German guide to the Sorento XM 2.4 GDI associates them with loss of power and higher consumption and recommends using cleaning additives regularly.

2.0 CRDi (D4EA)

In Elantra I, Santa Fe I, Santa Fe II, Trajet and Tucson I

- Medium severityFrequency: OccasionalInjectionCarbon build-up in the common-rail injectors with town drivingThe common-rail injectors of the 2.0 CRDi D4EA can build up carbon with town driving and short journeys, making cold starting harder; it is documented for the Hyundai Tucson I and it is reasonable to expect it in the other cars with this engine.

Smartstream 1.6 T-GDi

In Kona I, Kona II, Santa Fe IV and Tucson IV

- Low severityFrequency: RareIntakeCarbon build-up on the intake valves due to direct injectionBecause the petrol is injected directly into the cylinder, nothing cleans the intake valves and they can accumulate carbon over the miles. It is a general characteristic of direct injection; we have found no data specific to the 1.6 T-GDi Smartstream.

Common causes of P0505 on any make

From most to least likely, according to the sources.

1Dirt and carbon on the throttle body, which restrict the fine air flow needed for idle. AutoDTCs identifies it as the most common cause, and Samarins also lists it.^[1][2]
2Unmetered air entering the intake: cracked or loose hoses, loose clamps, or a gasket on the intake manifold or throttle body.^[1][2]
3Faulty PCV valve or crankcase ventilation hoses that leak, have collapsed or are blocked.^[1][2]
4IAC valve or its motor dirty, sticking or stuck, or idle air passages blocked, on engines that have one. Samarins comments that these valves fail very often.^[2][3]

What to check first

The first diagnostic steps, from the most likely and cheapest to check to the most expensive.

1Read all the codes first. Samarins recommends checking any other codes first, and AutoDTCs reminds that many of them disable the idle monitor.^[1][2]
2Look for manufacturer technical bulletins for your model: Samarins cites several for Honda, Ford and Toyota, some related to the IAC valve or the throttle body.^[2]
3With the diagnostic equipment, look at the actual idle speed and the target live. If the code appeared just after changing or disconnecting the battery, try the idle relearn procedure, which varies by car. AutoDTCs adds that if the code appears just after a control unit reset, a hot driving cycle should be completed before continuing the diagnosis.^[1][2]

Full guide to P0505: symptoms, diagnosis and whether you can drive

Frequently asked questions

Which Hyundai engines have faults that can trigger P0505?

1.6 GDI / T-GDI (1 fault), 1.0 T-GDI (1 fault), 1.1 and 1.4 CRDi (1 fault), 2.0 / 2.4 GDI and T-GDI (Theta II) (1 fault), 2.0 CRDi (D4EA) (1 fault) and Smartstream 1.6 T-GDi (1 fault). Each fault has its own page with the affected years and versions, the symptoms and the repair cost.

What does code P0505 mean on a Hyundai?

Idle control system: malfunction. The control unit fails to regulate idle: the actual engine speed deviates from the target it calculates itself. The code does not distinguish whether idle is too high or too low (P0506 and P0507 are for that) and does not point to the faulty part. Samarins gives a typical idle of 650 to 750 rpm on most cars as a guide. It is a generic OBD-II code: it means the same on a Hyundai as on any other make.^[1][2][3]

Can I keep driving with P0505?

Garage soon. AutoDTCs rates it as medium severity: it is not immediately dangerous, but unstable idle can make the car stall in traffic, which is why it advises repairing it within a week. CarWiki, which reduces it to a fault in the idle valve or its supply, does not rate the severity, but lists the engine stalling at idle or shortly after starting among the symptoms.^[1][3]

Sources

Every fact on this page links to its source. If you find an error, let us know.

P0505: Idle Air Control SystemAutoDTCs · Technical documentation · consulted 31 October 2026
P0505 Idle Control System MalfunctionSamarins.com · Technical documentation · consulted 31 October 2026
OBD Fehlercode P0505CarWiki.de · Technical documentation · consulted 31 October 2026 · in German