P0507 means the engine is idling higher than the computer is asking for. Almost always that is extra air getting in that nobody metered: a leak, or a throttle that is not closing as far as it should. Usually OK to drive, get it checked soon. Indicative UK repair cost is £40 to £250.
This code deserves more attention than its severity rating suggests, for one reason that applies to no other code in this library: the fault it describes is itself a named MOT defect. Everywhere else on this site, the honest answer about the MOT is that the warning lamp is what fails you. Here the raised idle is written into the inspection manual in its own right. More on that below, because it changes the order in which you should deal with this.
Can I drive with P0507?
Usually OK to drive, get it checked soon. There is nothing dangerous happening under the bonnet. A high idle is mostly a nuisance: the car creeps against the brakes in traffic, drive engages with a lurch, you use more fuel than you should sitting still, and the engine sounds busy when it ought to be quiet. The one thing worth saying about it is that an engine idling fast is an engine whose brakes have to work a little harder to hold it, and if the idle is high enough that you can feel the car pushing when you stop, get it dealt with sooner rather than later.
What P0507 means for your MOT
Two routes, and the first one is unusual enough to put ahead of the lamp.
- The idle speed itself. The DVSA MOT inspection manual lists, among the emissions defects, an engine that is "idling clearly above its normal idle speed". That is a major defect on its own terms. It is there because the emissions reading is taken partly at a settled idle, and an engine running fast distorts it. So this is the one code on this site where you can fail the test on the symptom, with no reference to any warning light at all.
- The lamp. As ever, a major defect under section 8.2.1.2 for petrol cars first used on or after 1 July 2003 and 8.2.2.2 for diesels first used on or after 1 July 2008.
And there is a third, indirect one. The extra air causing the high idle is usually an induction leak, and the manual makes an induction leak that could affect emissions levels a major defect under section 8.2.1.1. A split hose that the tester can see is a problem whether or not it has upset the idle.
What usually causes it
- A vacuum or intake leak. The headline cause, and the list of places is longer than people expect: a perished crankcase breather hose, the brake servo hose and its one-way valve, the hose to the fuel pressure regulator, a dipstick that is not seated, and on some engines an oil filler cap whose seal has hardened.
- A dirty or sticking throttle body. The mirror image of the low idle fault. Here the plate is being held very slightly open, by carbon on its stop, by a sticking spindle, or by a return spring that has weakened.
- A faulty PCV valve. The crankcase ventilation valve is a metered path into the inlet by design, and when its diaphragm splits it becomes an unmetered one. On several engines a split PCV diaphragm is the single most common cause of this code.
What it costs to fix in the UK
£40 to £250. A hose or a PCV valve is the bottom. A throttle body clean with the adaptation reset afterwards is the lower middle. A replacement PCV housing, which on some engines comes as part of the rocker cover, or a replacement throttle body, is the top.
A smoke test of the inlet is the standard way a garage finds the leak, and it is quick. What a car diagnostic costs in the UK gives you the going rate so you can tell a fair quote from an optimistic one.
These are indicative UK ranges for guidance only. Actual causes and prices vary by vehicle, and a stored code points to a system, not always the exact part.
What to check first
- Do the free test first: the oil cap and the dipstick. With the engine idling, make sure the oil filler cap is fully home and the dipstick is properly seated. On a number of engines a loose cap or a dipstick sitting proud is enough to raise the idle on its own, and the fix is to push it in. If the idle drops as you seat them, you have both found and fixed it in under a minute.
- Work round the breather and servo hoses with the engine running. Squeeze each one and watch the idle. A hose that changes the idle when you pinch it is either split or leading somewhere it should not. The brake servo hose is worth pinching specifically, because its one-way valve fails more often than the hose does.
- Check the PCV. Where it can be reached, see whether its diaphragm holds. Where it cannot, the smoke test is what will find it, and this is the point at which paying someone is sensible.
- Look at the throttle plate and its stop. Confirm it closes fully and springs back cleanly by hand with the engine off. Carbon on the stop face holds the plate open by an amount too small to see but large enough to matter.
Related codes
- P0506, idle speed lower than expected. The opposite condition, and the page that explains why a throttle body clean needs an adaptation reset afterwards.
- P0171, system too lean (Bank 1). Very often stored alongside this one, because the unmetered air raising your idle is also leaning out the mixture, and that page has the test that locates the leak.
- P0174, system too lean (Bank 2). Useful on a V engine, because whether one bank or both have flagged tells you where in the inlet the leak sits.
Get it narrowed down before you spend
A stored code tells you which system is unhappy, not which part has failed. If you want it narrowed down before you spend anything, send the code and your symptoms and a mechanic will read them personally. Quick Diagnosis is £20, and if we can't help, you don't pay.
Written by the First Diagnostic mechanic. Over a decade in the trade: a VW-only workshop running diagnostics and electrical repair, then BMW-only through to full engine rebuilds. Now an independent all-makes workshop, plus building and wiring drift cars for competition, including trackside work as head mechanic. More about who reads your codes.