P0505 🟡 Moyen ✅ Can drive (carefully)

Idle Control System Malfunction

The idle control system (idle air control valve or electronic throttle body) is not responding correctly. Common on vehicles over 60,000 miles.

💷

Average repair cost

£8 — £180

🔍 Symptoms

  • → Rough or low idle
  • → Stalling at idle
  • → Idle hunting (revs going up and down)
  • → Hard starts

⚙️ Common Causes

  1. 1Dirty throttle body (main cause)
  2. 2Faulty idle air control valve (IAC)
  3. 3Faulty throttle position sensor (TPS)
  4. 4Air leak

🔧 Recommended Fixes

  1. 1Clean throttle body with throttle body cleaner (~£8) — often fixes it immediately
  2. 2Reset ECU learning after cleaning (disconnect battery for 10 min)
  3. 3Clean or replace IAC valve (~£25-70)

🛒 Recommended Parts (Amazon UK)

Throttle body cleaner spray~£7-10
View on Amazon UK →
Carb and intake cleaner~£8
View on Amazon UK →
Throttle position sensor TPS~£18-45
View on Amazon UK →

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Frequently Asked Questions

Can I clear this code without fixing it?

Yes, but it will return if the underlying issue isn't fixed. Clearing a code only tells you if the problem is permanent or intermittent.

Will this code fail an MOT?

Probably yes if the check engine light is on during the MOT. The MOT checks OBD readiness monitors since 2018.