P0505 Code Meaning and Next Steps

First checks take 10 to 20 minutes for the first checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The engine stalls repeatedly or will not stay running at idle.
!The vehicle loses power badly enough that it becomes unsafe to continue.

If the light is steady and the vehicle still drives normally: Often yes for a short time, but idle quality should be watched closely.

What to check first

Step-by-step checks

1
Free - no tools
Check whether the engine stalls at stops, idles too high, or hunts up and down
2
Free - no tools
Inspect the throttle body, intake boots, and vacuum hoses for obvious leaks or sticking
3
Basic tool needed
Notice whether the code appeared after battery work, cleaning, or intake repairs
4
Basic tool needed
If scan data is available, compare commanded idle to actual idle before replacing parts
5
Basic tool needed
If the throttle body is dirty, clean and relearn it before moving straight to replacement

If the code returns

-If the idle improves after a cleaning or leak repair, the problem was probably airflow-related.
-If the code returns after a reset, the idle control side or a hidden vacuum leak becomes more likely.
-If the engine is also misfiring, fix that first because it can upset idle control on its own.

Background

What this code means

P0505 is a generic OBD-II idle-control code.

These codes usually mean the ECU is not able to keep idle speed where it wants it, either because the air path is off, the throttle body is dirty, or a related sensor signal is not believable.

The engine may idle too high, too low, or stall when you come to a stop.

Diagnosis

Common causes

Most common

Dirty throttle body

Carbon buildup can keep the throttle from managing idle correctly.

Common

Vacuum leak

Extra unmetered air can push the idle out of range.

Common

Idle-air control issue

The control side may not be able to adjust idle fast enough.

Possible

Throttle adaptation problem

Some vehicles need a relearn after cleaning or battery loss.

Avoid these mistakes

What not to do

xDo not replace the throttle body first if the intake is dirty, leaking, or obviously sticking.
xDo not ignore vacuum leaks, because they can mimic a bad idle-control part.

Parts

Parts that may need replacing

PartTypical costNotes

Throttle body cleaning or service$10-$120Often the right first step if the throttle is dirty.

Vacuum hose or intake repair$10-$120Worth checking if there is a visible air leak.

Idle-air control valve or throttle body$60-$350Relevant when the idle hardware itself is not responding.

Related OBD codes

P0506

P0506 usually means the idle speed is lower than the ECU expects.

P0507

P0507 usually means the idle speed is higher than the ECU expects.

P0171

P0171 usually means bank 1 is running too lean.

P0300

P0300 usually means the engine is detecting random or multiple-cylinder misfires.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0505 was expanded around common idle-control faults, especially throttle contamination, vacuum leaks, and idle-air control problems.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0505 - P0505 Usually Means the Idle Control System Is Not Holding Normal Idle Speed