Peugeot 3008 II: Flickering Check Engine Light and Rough Idle — What It Really Means

First, the important bit: a flickering light is not the same as a steady one

On your 3008 II, a check engine light that blinks or flickers is the ECU telling you something quite different from a steady lamp. A steady light means "I've logged a fault, get it looked at soon." A flashing light almost always means an active misfire — unburnt fuel is being pushed into the exhaust and cooking your catalytic converter. Combined with a rough idle, that picture fits a misfire on one or more cylinders, and it's the kind of fault where a few days of ignoring it can turn a £150 repair into a £1,200 one. The good news is that the 3008 II is a well-documented car and the usual suspects are fairly predictable.

Likely causes, roughly in order of probability

• Ignition coils and spark plugs — by far the most common cause on the 1.2 PureTech petrol. Coil packs fail with heat and age, often intermittently at first, which is exactly why the light flickers rather than staying on.
• Wet timing belt degradation (1.2 PureTech) — the belt runs in oil; as it wears, debris can partially block the oil pickup, hurting cam timing and compression. A rough idle that comes with a rattle or a delay on cold start deserves a close look here.
• Carbon build-up on the intake valves — direct-injection engines like the PureTech and THP don't wash their valves with fuel, so deposits build up and cause lumpy idle and misfires, especially from cold.
• Vacuum leaks and the PCV diaphragm — a split breather hose or a tired valve cover diaphragm leans out the mixture, giving a hunting idle and sometimes a whistle.
• Fuel delivery — a tired high-pressure fuel pump (common on the 1.6 THP), clogged injectors or a restricted fuel filter will all produce lean misfires under load.
• Diesel-specific (BlueHDi) — sticking EGR valve, leaking injector seals, or a blocked DPF mid-regeneration can all give a rough idle, though a truly flashing light is less typical here.

What I'd check first, in this order

• Read the codes properly — not just a generic scanner. You want P0300-series misfire codes, the per-cylinder misfire counters and the freeze-frame data. That tells you whether it's one cylinder or all of them, and at what temperature and load it happens.
• Swap-test the ignition — move the coil and plug from the misfiring cylinder to another. If the misfire follows, you've found it for the price of a coffee.
• Check the plugs' condition — oil-fouled, black, or worn electrodes all tell a story about what's happening upstream.
• Smoke-test the intake for vacuum leaks and inspect the breather hoses and PCV diaphragm.
• Compression and leak-down test if the misfire won't move — this is where you rule in or out valves, rings and timing.
• Fuel trims and rail pressure on a live-data road test to catch a weak pump or lazy injector.

Is it safe to keep driving?

Honestly — no, not for long. If the light is flashing continuously, pull over safely and get recovered; you're actively damaging the catalyst and risking unburnt fuel washing the cylinder bores. If it flickers only occasionally at idle and the car otherwise drives, you can carefully nurse it to a garage — keep the revs low, avoid hard acceleration and motorway speeds, and don't leave it a fortnight. And one small practical tip: on these cars, a weak battery or a dirty earth can throw odd electrical gremlins too, so make sure the basics are sound before you start replacing parts.

This material is AI-generated and for informational purposes only — it does not replace an in-person diagnosis by a qualified mechanic.