Many owners of late model Mercedes-Benz cars equipped with 3.0 and 3.5l V6 engines (M272 or M273) have been experiencing similar problems in performance lately, which include poor idle, loss of power, and a check engine light with the code P2006 (and sometimes others).
The problem is caused by an air flap inside this Mercedes-Benz intake manifold breaking, causing unexpected low acceleration depending on the orientation of the flap that has broken. To thoroughly understand what is going on here, let’s review what the system is doing and why variable-intake-runner intake manifolds are becoming so popular with many modern cars.
The intake manifold sits on top of the engine, and is the method by which the engine “breathes” or gets air inside of it. Connected to the intake manifold are individual “runners” going to each cylinder of the engine. As the intake valve closes, the air going into the engine hits the back of the valve and ‘bounces’ back. The pressure wave will ricochet back up into the intake manifold until it hits the back, where it will bounce back down the runner. The trick is to have the pressure wave arrive back at the cylinder right as the valve opens, achieving the densest possible air mixture passing into the combustion chamber (picture a high pressure standing wave right behind the open intake valve).
To have this effect (also known as scavenging, or if you really want to get a bit technical, Helmholtz Resonance) work in the RPM range you are targeting, you can tune the intake runners to be a very precise length. Unfortunately, scavenging only works in a narrow RPM range, so most engine designers build the intake runners to achieve this in a very useable RPM range.
For a road car, this is around 3-4,000 rpm, where long intake runners promote a smooth even vortex. A variable length intake runner manifold can switch between two sets of intake runners with a flap built into the manifold. This way, you can have one set of intake runners optimized for when the car is idling, and picking up low RPM speed.
If you get on the throttle and request power for sportier or more demanding driving, the flap switches over to the second set of intake runners that is optimized for the higher rpm range. Many of these intakes also have specifically shaped flaps that causes a vortex, adding even more efficiency.
The most common part to fail on the Mercedes manifold is one of the actuators for the variable system, causing the interior flap to become disconnected. We can repair some of these intake manifolds, rather then replacing them, but that is on a case to case basis. In any case, we can save you considerable money over what the Mercedes dealer charges, often as much as $1,000. Most failures are caused as the intake gets gunked up with oil and crud that comes out of the PCV system. The accumulated crud and sludge make he flaps have to work harder and harder.
Once the vehicle gets on in miles, the resistance on the actuators and flaps running this system (they are maintaining an airtight seal after all, so they are constantly moving along the walls of the manifold) becomes too much, causing the weakest part to break. In this case, its the cam lever in the center of the whole thing. Other parts can fail as well, including the flaps inside, the actuator mounting arms, and the vacuum diaphragms. In the past we’ve seen other shops just replace the plastic parts, but it invariably just fails again, unless the intake manifold is properly cleaned out and serviced. Keep in mind that if the arm does break and you replace just the actuator arm, the manifold will still be gunked. The resistance on these components against the manifold wall will continue to increase unless you thoroughly clean the manifold out.
Operating To Prevent Failure
Here are ways to avoid intake manifold failure in your Mercedes:
1. Have frequent oil changes using quality oil. We recommend oil changes at least every 5,000 miles.
2. After driving (once you have reached your destination), let your vehicle idle for a couple of minutes, rather than turning it off right away. This will let the engine cool down a little before turning it off.
3. Cleaning, we suggest cleaning the intake manifold every 40-60K miles, so we can prevent problems
4. Frequent maintenance. Have a qualified Mercedes service facility inspect your inspect your vehicle’s intake system every 6 months. At Atlantic Motorcar, we do this each time your car is in, as part of our normal service process.
Your Advocate, On Your Side
At AMC, because we are independent and locally owned, we are YOUR advocate, and our team makes a point of checking recalls and service campaigns from the manufacturer on every visit, and keeping our customers up to date.
Not a simple repair, yes, but one, if done correctly, will last several years. That’s our goal with Mercedes, and other autos here, fix it right the first time, and prevent problems from happening in the first place. 30 years of service experience have well taught us that “an ounce of prevention is worth a pound of cure.” Be cured, once and for all, and give us a call, we’re happy to answer any service questions you might have on your BMW, Audi, Mercedes, Lexus, Volvo or Volkswagen.
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If you have questions, or if we can be of further assistance, just call us at (207) 882-969, we’d love to meet you, and your car!
Bruce and the AMC Service Team