Idle speed higher than expected on Mercedes — M271/M274/M276 PCV diaphragm and vacuum hose.
Mercedes-Benz P0507 — Idle speed higher than expected on Mercedes — M271/M274/M276 PCV diaphragm and vacuum hose. Typical UK independent garage cost: £180–£580.
What actually causes P0507 on a Mercedes-Benz
Mercedes P0507 is PCV-related — diaphragm in the rocker cover or a perished vacuum hose. M271 cam cover is the famous one.
Mercedes-Benz engines that log P0507
- M271 1.8 Kompressor/turbo
- M274 2.0 turbo
- M276 3.5 V6
How we diagnose P0507 on a Mercedes-Benz
- Smoke-test intake
- Oil filler suction test
- Rocker cover PCV inspection
The common misdiagnosis to avoid
Cheap aftermarket M271 cam covers fail. Mercedes OE or quality Vaico only.
Mercedes-Benz P0507 repair cost in the UK
Expect £180–£580 including parts and labour at an independent garage. Main-dealer quotes on Mercedes-Benz are usually higher for the same job, and the spread exists because the cheap cause and the expensive cause throw the same code — pay for the diagnosis before you pay for parts.
Bob's workshop tip
M271 P0507 — cam cover with PCV. £180 part, hour's work.
Codes usually seen alongside P0507 on Mercedes-Benz
- P0171
Symptoms drivers report with P0507
- The car feels like it's 'creeping' forward too fast at traffic lights without touching the gas.
- Engine revs stay hung up at 1200rpm when you dip the clutch approaching an intersection.
- A noticeable 'hissing' or whistling noise from the engine bay when idling on the driveway.
- The stop-start system has stopped working because the idle isn't stable enough for the ECU.
- Surging or 'hunting' revs when you first start it from cold in the morning.
Repairs that clear P0507
- Smoke-test intake
- Clean throttle body
- Replace PCV valve / rocker cover
- Inspect all vacuum hoses
For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0507 guide.