⚠ P0505 MEDIUM SEVERITY

P0505: what it means

Officially? A wall of jargon. To most people? Absolutely nothing. That's exactly why we built the app.

The official definition vs. an actual explanation

Plug into any code reader and you'll get the same line every other app shows you. Technically correct. Practically useless.

What other apps tell you

"P0505: The idle speed control isn't working."

What OBD Mechanic tells you

"The engine's computer can't hold the idle where it wants it. On older cars a small idle air control valve does that job, and carbon build-up makes it stick. On most newer cars the electronic throttle does it, and a dirty throttle body causes the same trouble. You'll often notice a hunting, too-low or too-high idle, or stalling when you come to a stop. Cleaning is the cheap first move. After that look for an air leak, then the valve or throttle unit itself."

What actually causes it, cheap to dear

Worth checking in roughly this order. Don't jump straight to the expensive fix:

Carbon build-up in the idle air control valve or throttle body
Vacuum or intake air leak upsetting the idle
Idle air control valve failed, or its wiring or connector
Idle not relearned after the battery was disconnected or the throttle was cleaned (needed on some cars)
Electronic throttle unit fault (less common, and usually brings other throttle codes)

usually cheap depends pricey

Suggested checks

Clean the throttle body and, if your car has one, the idle air control valve. Do it with the ignition off, use proper throttle cleaner, and never force an electronic throttle open by hand
Check the idle relearn procedure for your car after cleaning or a battery change. Some do it themselves, some need a set routine
Listen for hissing and check intake hoses and breathers for splits
Check the valve's connector and wiring. If it's clean and still faulty, the valve or throttle unit is next

Which dials to watch for P0505

The code itself is a snapshot. The fault sets after the car's watched the numbers over a whole drive cycle. Here's what's worth keeping an eye on:

Engine RPM (live graph)

The heart of this fault. Watch the idle once warm: hunting up and down, sitting too high, or dipping hard when you stop all show what the control is failing to do.

Throttle (live graph)

On electronic throttle cars this shows how far the computer is opening the throttle at idle. A reading that creeps higher over time can point at a dirty throttle body.

Live simulation on the readings our free demo drive supports. This is how the app’s dials move.

It spots things you'd never see in the numbers

Codes rarely tell the whole story. The clever part is reading them together, and against your exact car. Here's the kind of thing it catches:

AI Mechanic

What our mechanic says

P0505

The engine's computer can't hold the idle where it wants it. On older cars a small idle air control valve does that job, and carbon build-up makes it stick. On most newer cars the electronic throttle does it, and a dirty throttle body causes the same trouble. You'll often notice a hunting, too-low or too-high idle, or stalling when you come to a stop. Cleaning is the cheap first move. After that look for an air leak, then the valve or throttle unit itself.

P0505: quick questions

Can I still drive it?

It depends how it's behaving. If it idles a bit high or low but doesn't stall, you can drive it, so book it in soon. If it stalls as you come to a stop or turn, get it looked at before you drive far, because a stall takes away the power steering and brake assist.

What will I notice?

A hunting idle, one that sits too high or too low, or stalling as you come to a stop. If the engine stalls on the move, the steering goes heavy and the brakes need a much firmer push. Pull over when safe.

Will cleaning the throttle body fix it?

Often, yes, especially on higher-mileage cars. Some cars then need an idle relearn before they settle. If it comes straight back after a clean, look for an air leak or a failed valve.

How much will it cost to fix?

A can of throttle cleaner is cheap and many people do it themselves. An idle valve is usually a modest part. A full electronic throttle unit is the dearer end.