An engine's hot intake valves are magnets for the carbon molecules splitting from fuel and oil vapors that waft up from the oil pan through the positive crankcase ventilation (PCV) system. Over time, the carbon bakes in place, interfering with air flow and preventing the valves from sealing properly.
There is an issue with the proliferation of direct injected engines that is slowly creeping up in more and more discussions on message boards these days. Because these engines inject fuel directly into the cylinders, there is no fuel washing over the intake valves. There are detergents in most gasolines that help keep the intake valves clean. With Direct Injection, those detergents are essentially useless. As such carbon builds up on the intake valves and causes problems with Missfires, Check Engine Light and Rough Idle. It's not limited to one manufacturer either. I have seen it discussed at length on Audi, BMW, Hyundai, Kia, Mazda, Mercedes-Benz, Mini Cooper, Nissan, Lexus, Saab, Subaru and Volkswagen boards. Toyota has been employing a bastardized system where there are two sets of injectors. One direct and one port. Ford says that they have fiddled with the valve timing to avoid the issue but that remains to be seen.
We have found there is only one sure way to prevent this from occurring. Have us regularly perform Induction System Services. Click here to watch a video of our Induction Service process.
Unfortunately many vehicle manufactures imply that their vehicles need no “tune-up” type service for 100,000 or more miles. This is simply not true (see pictures 1 and 2). When the carbon build up gets this bad the intake manifold has to be removed and the carbon must be blasted with ground walnut shells using a special tool kit (see picture 3) or the engine must be disassembled and cleaned by hand.
Fortunately we have the equipment to perform the walnut shell cleaning. But we ALWAYS recommend our 3 part Induction Services as preventative maintenance, rather than waiting until the manual valve cleaning is needed. Preventative maintenance will save you a lot of TIME and MONEY in the long run…