Why is my Bentley Continental GT misfiring or idling rough?

Short answer: On an early Continental GT, misfire and lean codes very often come from old plastic vacuum and breather (crankcase vent) hoses that crack with age and let in air the engine doesn't measure. Owners also find worn plugs, corroded coil packs and damaged wiring. A smoke test (a shop blows harmless smoke into the intake to show leaks) is the best first step. Some hoses are easy to reach. On some cars, the ones behind the engine mean pulling the engine.

Symptom: A check engine light with P0300 (random misfire) or cylinder misfire codes, lean codes for one bank, a rough or chuffing idle, or a stumble when cold.

What to check first

1. Get a smoke test for vacuum leaks. Owners on 6SpeedOnline found split hoses this way that they couldn't see by looking.
2. Look at the breather hoses under the air box. One owner found a cracked breather pipe and a broken wire on the mass airflow (MAF) sensor plug, the sensor that measures air coming into the engine.
3. Pull the plugs and look at the coil pack plugs. Green corrosion and broken connector clips can cause misfires too.
4. Check both batteries. These cars have two, and low voltage causes strange faults.
5. Ask the shop which vacuum layout your car has before quoting an engine-out job. Early cars and later cars route the lines differently.

Likely causes

1. Cracked plastic vacuum or breather hoses. The most common find. Cheap parts, but some are hard to reach.
2. Worn spark plugs or corroded coil packs. Plugs on the lower bank often look worse.
3. Damaged MAF sensor wiring or connector. A broken wire gives wrong airflow readings.
4. Vacuum lines on top of the transmission (some early cars). On some early cars these lines sit where the engine and transmission must come out to reach them.

What it usually costs

The hoses themselves are inexpensive. One owner rebuilt the breather lines with 3/8-inch oil cooler tubing. The big cost is labor: on cars with the vacuum lines over the transmission or along the back of the engine, owners and dealers have pulled the engine to replace them, which is a very large bill. Get a smoke test and a clear quote first. We don't have a reliable dollar figure to share.

Is it safe to keep driving?

Usually drivable gently for a short time, but a flashing check engine light means a bad misfire that can overheat the catalytic converters. Don't drive hard or far with it flashing. Verify with a mechanic.

DIY or shop?

Shop for the smoke test and hidden hoses. Plugs, coil plugs and the easy breather hoses are doable at home with a good scan tool, but the W12 is cramped.

Recalls, bulletins and complaints in plain words

• Recall 08V217 (2004–2008 Continental GT, GT Speed, GTC and Flying Spur): road salt could corrode the fuel filter housing and cause a fuel leak. It isn't the misfire cause, but if your car is part of this recall, the dealer fixes it for free.
• NHTSA complaints: 4 keyword-matched complaints for Bentley Continental GT/GTC/Flying Spur 2004–2011 (of 9 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-21; keywords: misfire, vacuum, hose, stall, rough idle, check engine, hesitation) (NHTSA returned no complaint data for 13 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In Bentley GT 2007 multiple misfire P0300 on 6SpeedOnline, an owner with misfires on both banks found a broken wire at the MAF sensor plug and cracked breather hoses on both sides. Members suggested replacing the brittle hoses with oil cooler tubing and checking the coil packs for corrosion. New plugs cut the codes down, and the owner went on to replace connectors and check the batteries.
• In 06 GT with split vac hose issues on 6SpeedOnline, a 26,000-mile 2006 GT had lean and misfire codes on one bank. A smoke test found a split main vacuum line, two cracked hoses going to the intake, and a split line behind the steering rack. Members explained that some hoses can be done in the car but the lines on top of the transmission on some early cars need the engine out.

My take

If you're shopping for a used Continental GT, ask whether the vacuum and breather hoses have been replaced and get a smoke test before you buy. It's one of the first things these cars need.

Vehicle focus: 2004–2011 Bentley Continental GT, GTC and Flying Spur with the 6.0 W12.

Safety / mechanic note

A flashing check engine light means a severe misfire that can damage the catalytic converters. Verify with a mechanic.