I recently purchased a 2007 r320 that has 130000 miles on it. It was meticulously maintained and runs well but has recently went into limp mode(light?) and is showing po299 code. When cleared car preformed normally for a very brief time then code and limp mode returned.
What should I check? I am by no means a mechanic(a carpenter!). My mechanic is puzzled!
Thank you.

Looking it up on google I see the code has something to do with "turbo underboost". But knowing the code doesn't really help. From the little I could find on it, it would seem checking all connections and the MAF sensor might help, also finding air leaks in the ducting leading from the turbo to the intake. There's a reason most of us stick with the old stuff, less complexity, heck even some of prefer the non-turbo for even less complexity yet.

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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission.

2007 ml320cdi codes - Mercedes-Benz Forum

Watch the video in the above post. It is something to look at to confirm or eliminate.

Attached Thumbnails

 

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Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

I ought to have added... A day prior to experiencing this problem(limp mode and po299 code) I put fuel(yes, diesel!) in while the car was running. The next day the check engine light came on and that's when we first saw the po299 code come up. My mechanic reset the car and the check engine light has not come back on but the car quickly went back into limp mode. We've checked all of the connections to the turbos and all looks fine. I have thoroughly checked to make sure the fuel filler cap is on properly.
Help!

Just throwing this out there as a theory because I have no direct experience:

I believe this car has a variable geometry turbo. It's not uncommon for VGT's to hang up (again, no experience with this one). You might want to do some research as to what turbo your car has and if it's prone to sticking.

If the nozzle is wide open, this would certainly cause a low boost condition for a short time if the throttle is rapidly applied at lower RPMs.

EDIT: I just read through the information in post #3 and viewed the video and that's what I'm talking about. Sorry for the repeat information.

Here's a link to the video in YouTube. There are some good comments there as well.

http://youtu.be/iZvQkROd4Uw

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Kartek
Thanks so much! I'm honestly so ignorant of mechanics that I understand very little of what you've said but my mechanic will!