Common causes of P0243 code in w210 E300D?
 

Mine has started recently setting the P0243 (wastegate solenoid malfunction) code occasionally, which means no boost and it makes the car too slow to merge onto the freeway safely (ill-advised metering lights mean merging onto the freeway is often a full throttle 0-75 mph exercise to avoid getting run over by a semi truck in the places I regularly drive).

But anyway, from a google search there are so many things (MAF, waste gate solenoid, actual wastegate, catalytic converter, egr, various vacuum lines, etc) that can cause this I could probably buy another car for cheaper than just replacing stuff until I guess right. Has anyone has this happen and actually fixed it? I have found that with most extremly hard to diagnose problems asking someone else how they fixed it is usually the best place to start.

These cars have two identical vacuum transducers - electrical signal varies the amount of vacuum applied.

The one on the drivers side just behind the washer tank is the EGR actuator.
The one on the passenger side on the side of the air cleaner box is the waste gate actuator.

Swap the transducers side to side and see what happens.

I was having a similar issue where the code would come up every few weeks, then clear. One of my coworkers suggested I buy an $8 can of CRC MAF Cleaner and spray down the MAF sensor. The light hasn't come on for about 2 years now and the car is running as strong as ever.

Thanks for the suggestion, it turned out that even though looking at them they seemed fine, one of the rubber ends of the vaccum lines was totally rotten and fell apart when I took it off. I imagine that was probably the problem.

So swapping the 2 vaccum transducers, cleaning the MAF and replacing the cracked vaccum lines did not help. It still sets the same code almost every time I drive it when merging onto the freeway.

Does anyone else have any suggestions? I would really like to get it so I can drive it safely again, but from what I have read whatever is causing it can be extremly difficult to impossible to track down so I am not really sure the best way to go about checking everything. If I knew what the problem was I am sure I could fix it without much trouble, but I don't really know what else to check.

Test the wastegate solenoid. It's vacuum actuated, so should be easy to test.

Look at the hose to the map sensor, its mounted on inner wing and connected to the inlet manifold by a short barely long enough hose-- which could mean tired engine mounts let the engine move and expose cracks loaing vacuum/ pressure.

If one hose went bad a fair chance others are.

Where is the MAP sensor located? I doubt that the solenoid is bad because I switched it with the EGR one and nothing changed.

MAP sensor is on the inner firewall on the drivers side; other side of the wall from the brake booster.

The hose goes to a fitting in the intake manifold. It is under the "rack of ribs".

If this hose falls off, the system cannot tell how much boost is being provided so the computer dumps the waste gate. This kills your boost and makes the car run like a slug.

Two hoses on the egr valve body, one is the vacuum to operate it (thicker hose) and the other goes to the map sensor (thin hose similar to injector leak off size.
Look at the engine from the front and map sensor is at 2-3 oclock position.