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Discussion Starter · #1 ·
Van lost power on freeway and threw a turbo underboost P0299 code. I believe it went into limp mode at that time. Anyways i ended up pulling the charge air hoses off the intercooler and throttle body to inspect for cracks. They all look good to me and the rubber o-rings still intact. At that time i noticed MAF sensor was filthy so i cleaned that and cleared the code and went for a 4 mile drive and then another. So far So good. But...............anyways, anybody else have any turbo issues besides me?
 

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Discussion Starter · #3 ·
You checked the most common cause, but you also need to check the waste gate. If it sticks open that will underboost as well. Do NOT oil it with improper stuff unless you like setting your vehicle on fire.
Yeah, i saw the waste gate valve. I didn't mess with it as it's hidden under a heat shield. Is the valve serviceable without removing turbo and what type of waste gate is it? Vanes or just a flapper?
 

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I would normally say check the MAP sensor and it’s wiring, except the van likely wouldn’t run without that working well.
Otherwise it may have been an early warning of a turbo going out if this was underboost during a throttle transient (acceleration). If the turbo is lagging that is an early indication of it going out, though normally a fairly small sign. I’m not sure how sensitive these engine are.
 

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Discussion Starter · #6 ·
I would normally say check the MAP sensor and it’s wiring, except the van likely wouldn’t run without that working well.
Otherwise it may have been an early warning of a turbo going out if this was underboost during a throttle transient (acceleration). If the turbo is lagging that is an early indication of it going out, though normally a fairly small sign. I’m not sure how sensitive these engine are.
After another P0299 code thrown. I decided to do some troubleshooting. Turned out to be the vacuum actuator leaking by and never fully seating the waste-gate. A quick pull with a mighty vac handheld vacuum pump identified the problem. Of course Mercedes doesn't sell the actuator separately AFAIK. But, i was able to obtain one from China off ebay after a long wait. (first shipment lost). Anyways, If it doesn't hold up i'll get one from Mamba.
 

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Great fix kbcool! The stealership would probably hose you and say the entire unit including turbo has to be replaced....and we found a small crack on the exhaust manifold, so that's a another $3000. Lol.

That's great the arm is the same lenth.
 

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After another P0299 code thrown. I decided to do some troubleshooting. Turned out to be the vacuum actuator leaking by and never fully seating the waste-gate. A quick pull with a mighty vac handheld vacuum pump identified the problem. Of course Mercedes doesn't sell the actuator separately AFAIK. But, i was able to obtain one from China off ebay after a long wait. (first shipment lost). Anyways, If it doesn't hold up i'll get one from Mamba.
did the new wastegate solve your problem? My Metris started to develop similar symptoms and threw a code. Initial inspection of the piping looks good so I am trying to diagnose the cause of the under boost.
 

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Discussion Starter · #9 ·
did the new wastegate solve your problem? My Metris started to develop similar symptoms and threw a code. Initial inspection of the piping looks good so I am trying to diagnose the cause of the under boost.
Yes, it solved the problem. To diagnose without guessing, you need to connect a handheld vacuum tester to the actuator diaphragm and see if it moves the wastegate arm fully and holds it without leaking. Mine would just barely move as i pumped it and immediately leaked out. It felt like i was putting air into a tire with a big hole in it. Heres a link to the tester i bought. Amazon.com: Mityvac MV8510 Silverline Elite Hand Pump : Automotive
 

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Just want to chime and thank kbcool for posting this. I had similar symptoms at 109k, proceeded by increasingly bad fuel economy (like 15 mpg) before it finally started limping and throwing codes. Was able to find the wastegate actuator on eBay from a domestic source, and am big time relieved it wasn’t the whole turbo!
 
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