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I have a 2012 VW Tiguan 2.0T with 80k. I just had maintenance done and just one month later the engine light came on. I went to the dealer and they told me my car needs a manual intake decarb, which will cost me around $1000. I have the following questions:

1. Whether I should decarb the car engine now

2. Which way is better, walnut blasting or chemical?

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- Jessica

Direct injection engines, such as in your Tiguan, suffer from excessive carbon buildup on the backside of the intake valves. As the carbon continues to build, the intake valves will loose their ability to effectively seal their respective combustion chamber. An engine misfire will then develop, eventually turning on the engine malfunction light.

A manual intake decarbonization typically entails the complete removal of the intake manifold so that the back of the valves can be accessed and serviced. Less invasive crushed walnut shells are used as an alternative to sand to blast the carbon away from the back of the valves.

Alternatively, a technician will use a fogging machine that delivers strong chemicals directly into the intake manifold while the car is running. This process will soften the carbonm, causing it to breakdown and be burnt by the engine.

Your malfunction engine light is illuminated because your engine is misfiring and needs attention. The chemical process is very effective as preventive maintenance, while the walnut blasting is used as a catch-all service, but either process can be used to solve your particular problem.

Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing “Lou’s Garage” in the subject line.

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