I have a 313cdi 2001 which i basically didn't drive for six months. When i started driving it again i had a problem with it not revving much past 3000rpm and also i would get abs edc and traction light coming up intermittently with the abs cutting in in dry weather when not needed.
Well i built myself up for a big bill at Birminghams main Merc van dealer where i used to take it and where i actually bought it from but then decided to have a change and take it to Andy Gayle independent merc mechanics.
I dropped it off at Andy Gayles and the same night it was fixed. Diagnosis was a split vaccuum pipe somewhere on the engine. Cost £104.00 inc.Vat. labour and some pipe.
The brakes were and are nothing to do with the power prob but funnily enough the abs edc lights etc come on still but so little in frequency that i'm not that bothered about it.
so just goes to show....try your independent!!! you can guarantee that if Birminghams premier merc van dealer had of got hold of it they have changed everything going until they'd cleaned me out!!
On the subject of Merc dealers..
I had the turbo and viscous fan changed 2 years ago by this same Merc van dealer spending the best part of £1500 and after finding that the viscous fan was staying on permenantly even at 90 on the motorway so i took it in and asked what they thought of the fact the viscous fan coupling which they had changed 2years ago had only lasted 9000 miles
.... The answer bring it in and well charge you to change it again
After some research i have removed the fan and am now driving round Fanless at between 80-90 deg c on the dash, i shall fit an elec fan in the summer.