The IAC valve or electronic throttle isn't holding idle correctly.
P0505 — also written PO5O5, P 0505, 0505 — is the OBD-II code for idle air control (iac) system. Same code, same fix: this page covers every spelling of it.
P0505 means your engine can't settle on a steady heartbeat, usually because the idle valve is gunked up with carbon or there's an air leak letting the engine 'breathe' behind the ECU's back. Common on older Corsas and high-mileage Hondas.
P0505 is a fuel & air fault code, typically costing £60–£400 to put right in a UK garage.
What P0505 actually feels like to drive
- The car 'kangaroos' or jerks when you lift off the throttle in slow traffic.
- Engine revs bouncing up and down between 800 and 1500rpm while sitting at the lights.
- Stalling out completely as soon as you dip the clutch approaching a roundabout.
- Idle stays high (about 1200rpm) even when the engine is fully up to temperature.
- A loud 'hissing' sound coming from the engine bay that stops when you turn it off.
What causes P0505?
- Sticking IAC valve
- Carbon-fouled throttle body
- Vacuum leak
- Failed throttle body motor
UK vehicles that throw P0505 most often
- Vauxhall Corsa C/D 1.2 & 1.4 (Z12XEP/Z14XEP) 2004-2012
- Honda Civic 1.6 VTEC (B16/D16) 1998-2005
- Ford Fiesta 1.25/1.4 Zetec (Sigma engine) 2002-2008
- Volkswagen Polo 1.2 3-cylinder (AZQ/BME) 2002-2009
- Renault Clio 1.2 16v (D4F) 2001-2012
- Nissan Micra (K11/K12) 1.0 & 1.2 1998-2010
How P0505 is fixed
- Clean throttle body properly and re-learn
- Replace IAC valve on older cars
- Fix vacuum leaks
The P0505 misdiagnosis that wastes money
I see it all the time—lads rushing to buy a brand new throttle body or IAC valve the second they see P0505. They’ll spend £200 on a VDO unit and the car still hunts at idle. Nine times out of ten, it’s a tiny vacuum leak on a perished breather pipe or a gummed-up butterfly valve. On those older Vauxhall Z16 engines, people swap the valve when it just needed the tiny breather hole in the manifold cleared with a bit of guitar string or a 1.5mm drill bit. Don't throw parts at it until you've checked for air leaks with a smoke machine or a bit of brake cleaner.
What a UK garage should charge for P0505
A basic diagnostic scan to confirm the code will set you back £50 to £80 at a decent indie. If it just needs a proper clean and a re-learn, you're looking at about £100 total. If the IAC valve itself is shot, a Bosch or Denso replacement part usually costs between £60 and £150, plus an hour's labour (£60-£90). If it’s a modern 'fly-by-wire' throttle body that’s failed internally, you could be looking at £300+ for the part. Main dealers will easily double these prices with their £150+ hourly rates.
P0505 repair cost in the UK
Most P0505 repairs land between £60–£400 including parts and labour. The spread is wide because the cheap fix (a sensor, a hose, a leak) and the expensive fix (a major component) throw the same code — which is why a proper diagnosis before parts are bought saves the most money.
Bob's tip on P0505
If your garage tells you that you need a new throttle body, ask them two things: 'Have you checked for vacuum leaks?' and 'Have you performed a throttle idle re-learn?' On modern VAG or Ford cars, if you disconnect the battery or clean the carbon off, the ECU gets confused and throws P0505. It needs a proper diagnostic tool (like VCDS or Snap-On) to tell the car where 'zero' is again. Don't let them charge you £400 for a part if a 10-minute software reset and a £5 tin of Wynn’s Throttle Body Cleaner would have sorted it.
Can you drive with P0505?
Yes but expect stalling.
Urgency: medium.