Toyota Mark X: 4GR-FSE 2.5 V6 intake valve carbon build-up (direct injection)

The 2.5 V6 in the Mark X 250G injects fuel straight into the cylinder, so no petrol ever washes over the back of the intake valves. Oil vapour drawn in through the crankcase breather bakes onto them instead, and the deposits thicken from roughly 100,000 km. The car does not break down; it gets progressively doughy, idles unevenly and eventually misfires, and because it happens over years most owners never notice how much has gone. These are Japanese imports with thin service history in New Zealand, so assume it has never been cleaned unless there is paperwork saying otherwise. Cleaning is labour, not parts.

• Uneven or shaky idle, especially when cold
• Hesitation or flat spot when accelerating from low revs
• Misfire or engine warning light in worse cases
• Fuel economy quietly worse than it should be

1. 1

   Start the car from stone cold and let it idle while you watch the tachometer and feel the car through the seat — a healthy V6 idles smoothly and settles quickly, and a shake or hunt that clears once warm is the classic sign.

2. 2

   On the test drive, accelerate gently from about 1,500 rpm in a mid gear and feel for hesitation or a flat spot before it picks up.

3. 3

   Take the oil filler cap off at idle and look for heavy fumes, which drive the deposits.

4. 4

   Ask the seller whether the intake has ever been cleaned and for any Japanese auction sheet or service record that came with the import.

5. 5

   Check the dash for an engine light, including one that appears only under load.

6. 6

   If a workshop inspection is possible: a borescope down the intake port shows the deposits directly, and a scan for misfire counts per cylinder will find what a short test drive misses.

Parts involved: PCV / oil separator.

$600 to $1,800 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.

• “Has the intake ever been cleaned, and at what mileage?”
• “Do you have the import auction sheet or any Japanese service records?”
• “Does it idle roughly when cold?”

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.