MajorCommonEngine

Porsche 911: Direct Injection Carbon Buildup on Intake Valves (991/992)

Direct Injection Carbon Buildup on Intake Valves (991/992) is a common engine fault on the Porsche 911 on the 2012 onward cars, and we rate it major. Putting it right costs $800 to $2,000 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 18 documented faults on the Porsche 911.

Vehicle: Porsche 911
Years: 2012 onward
Fuel: petrol
System: Engine

This page covers the Porsche 911 as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Porsche 911 faults18 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph of the PCV / oil separator yet. We would rather show none than show a picture of a different part.

What goes wrong

The 991 and 992 generation 911s use MA1 and MA2 turbocharged flat-six engines with direct fuel injection only. DI does not wash intake valves with fuel, so oil vapour from the crankcase breather accumulates as hard carbon deposits on the back of the intake valves. Over time carbon restricts airflow, causes rough idle, misfires, and power loss. Walnut blasting (media blasting with walnut shell abrasive) through the intake ports is the accepted remedy, typically required every 50,000-80,000 km. A failed oil separator markedly accelerates buildup.

What you would notice

Rough idle or hesitation on cold start
Misfires at low RPM or under light throttle
Gradual reduction in power or throttle response
Intake airflow or misfire fault codes in diagnostics

How to check it

Where to look. Back faces of intake valves and intake ports, flat-six engine

Review service history for walnut blasting intervals. For cars over 60,000 km without documented blasting, budget for the service. Check the PCV and oil separator system — a failed separator accelerates carbon accumulation and should be replaced at the same time. If a workshop inspection is possible: An endoscope through the intake port will show carbon on valve faces.

Parts involved: PCV / oil separator.

What it costs to put right

$800 to $2,000 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“Has walnut blasting of the intake valves been performed, and at what mileage?”
“Has the oil separator been inspected and replaced if necessary?”
“Are there any idle quality issues or misfires under light load?”

Now check the Porsche 911 you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.

Porsche 911 buyer questions

Is direct injection carbon buildup on intake valves (991/992) serious on a Porsche 911?

We rate it major and common on the Porsche 911. The 991 and 992 generation 911s use MA1 and MA2 turbocharged flat-six engines with direct fuel injection only. DI does not wash intake valves with fuel, so oil vapour from the crankcase breather accumulates as hard carbon deposits on the back of the intake valves. Over time carbon restricts airflow, causes rough idle, misfires, and power loss. Walnut blasting (media blasting with walnut shell abrasive) through the intake ports is the accepted remedy, typically required every 50,000-80,000 km. A failed oil separator markedly accelerates buildup.

How much does it cost to fix on a Porsche 911?

$800 to $2,000 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Porsche 911 years are affected?

Our research records this fault on the 2012 onward Porsche 911. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.