Surging low speed

[D3ady]

So here goes a few pointers of ideas wpuld be appreciated.
So driving along between 30-40mph and the car starts surging.
The rev counter is visibly going up and down.
And you can feel the car surging
Has anyone got any ideas on what this could be it doesn't do it when accelerating ect only when cruising at low speed
Any tips and advice would be appreciated

 

[Dickster]

It could be a variety of things I would guess, but I’ve had similar symptoms with three different cars and it was the throttle body.

 

[D3ady]

It could be a variety of things I would guess, but I’ve had similar symptoms with three different cars and it was the throttle body.

Mines a 2.1 cdi auto is yours same engine types

 

[Dickster]

No, completely different. I had similar surging issues on a 4 litre Jeep Wrangler, BMW X5, and a Porsche 911..

I’m not suggesting it is that but worth a look as they don’t last forever.

 

[Billwithdeadmerc]

My CLK 320CDI has been undrivable with engine surging when in gear. Various specialist and my main Merc dealer can't find the problem as there are no fault codes or warning lights.
The car is a write off, and no one can help.

 

[Alps]

prob gunked up throttle body, get it cleaned an see how it runs. If not that then there may be a vacuum leak, gasket, air pipe or something.

 

[Billwithdeadmerc]

I have removed the air intake ducting and found the throttle intake nice and clean.
I have replaced three fuel pressure sensors and valves, the front SAM, the battery, and had the correct software updates for the engine and gearbox ECUs and the SAM.
If the ECU faults and dash warning light are cleared, they do not return until the car had been driven for over 5 horrible/worrying miles.
The fault codes then are only two P2047 & P2017 which both are "Rail pressure monitoring via the Volume Control Valve is too low"
The valve has been replaced with a new Merc part to no effect.
If the car is in neutral the engine revs and performs perfectly. The CAM bus signals between the ECU and gearbox scope perfectly.
My Mercedes dealer ahs contacted Merc Germany who says it is beyond economic sense to spend any more money on it, i.e. scrap it.
At 77,000 miles this is such a great disappointment.

 

[Alps]

get it to a good indie... Ollie at PCS will be able to sort it...

 

[Billwithdeadmerc]

Can you give me his details please?