Mercedes C-Class Rough Idle

I have two issues with my car at present. I have just bought a 2002 Mercedes C-Class 270 CDi Elegance with 89,000 miles. This stood idle for a month before being sold to me. I knew when I bought the car that it had a rough idle, so I am not surprised with the symptoms. The vehicle has FSH and has been well looked-after, with all the receipts, etc. The car starts on a rough idle whether it is cold-started or after the engine gets hot. I haven`t had the chance to peek under the bonnet yet, but need to be directed towards the right area before I spend a month or two trying to find the cause.
So far I have added Cataclean twice to see if it would make a difference. The RPM is where it should be, and moves very slightly up and down, but not much else. The Cataclean seems to have taken the edge off the roughness, but a noise persists starts as a throaty sound and becomes more settled, but still rough and mixed with a little rattling sound. It shakes the vehicle a little, too. I have checked with an EOBD scanner, but there are no present or pending fault codes. In every other aspect, the vehicle is superb: acceleration, top speed, handling, etc.
Could there be an induction leak somewhere? Once the vehicle is cruising normally, there are no issues. I would have thought it would not be as smooth if there was a leak. The other issue is with the handbrake release mechanism, as it sometimes sticks and won`t release. Does it need cleaning and lubricating or is there a more sinister gremlin involved? K Carr

C-Class Parking Brake Pedal
C-Class Parking Brake Pedal
There are a few possibilities as to the cause of the rough idle. You may find that the problem is due to an injector fault or a problem with the MAF sensor. Although no codes come up with your scanner, you may find it worth getting the system checked with the Mercedes Star system. This may show up codes not accessible to the EOBD scanner.
As a starting point, I would check through all vacuum and induction piping. The fault could also be due to an air leak in the system, as you suspect, and the best way to find a leak is to systematically check through the pipes using a light. Normally, any breach in the system will leave a trace of oily residue around it.
The handbrake mechanism on the C-Class does not generally give many problems, but as yours has been standing for a short while, I would expect the mechanism to require lubricating. The splitter is situated under the rear passenger seat and I would lubricate this as well as the actual parking brake pedal mechanism. Another possibility is that one of the cables has worn and is grabbing internally. In this case, a new cable or cables will be needed.

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