At our shop, we see many cars with direct injection engines that have carbon build-up on the intake valves. Most recently, we had this BMW 335i in our repair shop. The customer was complaining that their vehicle was misfiring and running rough. We checked the intake valves and they were pretty gummed up. We safely removed all the carbon build-up by use of walnut shell blasting. Check out the before and after photos of the intake valves!
Carbon build-up is very common on engines that have direct gasoline injection systems. The carbon build-up is an end result of crankcase vapors (dirty leftovers from the combustion process) which also contains tiny engine oil drops. The dirty crankcase vapors cannot be allowed to escape into the atmosphere so they are routed to the intake manifold to be burned with the air fuel mixture and then further treated by the catalytic converter in the exhaust system. The vapors/oil mixture is supposed to be separated (oil separated from the vapors) prior to entering the intake manifold, but apparently this part doesn’t function very well or is a poor design.
The check engine light will turn on, the engine will run poorly at idle (due to air restriction), and there will be misfire faults for each cylinder in the engine control module. Note that installing fuel additive into the tank will NOT help. A very common scam is for auto repair shops to sell a fuel injection cleaning service as a fix for this but in truth it will not even remotely address the issue.
Aftermarket suppliers have designed a system that collects the vapors/oily mixture and directs them to a separate canister instead of the intake manifold. The only disadvantage is that the collection cylinder needs to be manually drained frequently and is not emission compliant.
Regular servicing can help catch and prevent this issue before you end up with a large repair bill. At Rennology Motor Sport, we specialize in engine carbon cleaning for Audi, BMW, Mini Cooper, and VW. Carbon cleaning can be completed in one day and returns engine performance to near new levels. Call to speak with a specialist and make an appointment today!