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A common fault with these engines is a split breather hose under the air filter housing & would start by checking this first. It is quite hard to get to - you can just about see it from the front of the engine under the filter housing, you may need to prise it apart gently to see if you can hear the engine note change or hear a hissing noise. If split it can often store faults that appear to be a faulty air flow meter.
The air filter housing needs to be removed to replace the hose.
Also check the rest of the intake for any air leaks.
The engine can also suffer from compression issues - ensure a compression test is carried out if the above is ok.
Best regards, Paul
Yes - if the air leak is bad enough! It can cause stalling, surging and/or rough running.
I cant believe a Mercedes dealer will not look at it if there is no codes stored! That really is just a starting point for diagnosing a fault!
I would inspect the hose to see if there are any air leaks. Use a small torch & look under the front of the air filter housing & you should see the hose.
just a follow up to see if you could give me any advice. MB have only just looked at my car today, they are saying it is nothing to do with the original repair. It's taken them an hour to decide that today at £100 plus vat. He thinks it 'may' be to do with the crankshaft? however the car hasn't lost any oil or gone through any recently? To get a proper diagnosis he wants another 3hrs at £300+vat. does this sound accurate?