Slightly lumpy idle, reduced throttle response and occasional hesitation....

DSM10000

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Having recently replaced the alternator, water pump and a/c condenser plus an MOT pass without any problems last week I was looking forward to a few months trouble free driving in the C320.

However, over the last couple of days the idle has become a little low and unstable (no stalling), throttle response is a little dull and, occasionally, there is a hesitation on applying throttle, especially if doing so having slowed and then accelerating.

I called into my MB specialist yesterday and although busy hooked it to Star, no obvious faults and no codes logged although it was a very quick diagnostic.

He thinks it is the MAF, unfortunately he is away for two weeks so cannot see the car until then. After 140,000 miles and with these symptoms he is fairly confident that it needs a new MAF. I have found a new Bosch replacement and will fit this, I may return it if it is not the cause.

Does this diagnosis seem reasonable? Fitting it seems simple, a plug and a clip holding it to the throttle body.

Thanks as ever!
 

Bernie C

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Sep 7, 2011
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Merseyside
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Mercedes C320 CDI Sport & SL320 R129
Having recently replaced the alternator, water pump and a/c condenser plus an MOT pass without any problems last week I was looking forward to a few months trouble free driving in the C320.

However, over the last couple of days the idle has become a little low and unstable (no stalling), throttle response is a little dull and, occasionally, there is a hesitation on applying throttle, especially if doing so having slowed and then accelerating.

I called into my MB specialist yesterday and although busy hooked it to Star, no obvious faults and no codes logged although it was a very quick diagnostic.

He thinks it is the MAF, unfortunately he is away for two weeks so cannot see the car until then. After 140,000 miles and with these symptoms he is fairly confident that it needs a new MAF. I have found a new Bosch replacement and will fit this, I may return it if it is not the cause.

Does this diagnosis seem reasonable? Fitting it seems simple, a plug and a clip holding it to the throttle body.

Thanks as ever!

Hi - I've had very similar issues and a maf did in fact cure the problems - at 140k it's definitely a good starting point - good luck with this and report back when you are sorted
 

martyz

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I would try the maf too,all the symptoms are there,I am sure you will have a result.
 
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DSM10000

DSM10000

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The replacement MAF arrived earlier this week so I decided to try it out this evening. I removed the electrical plug and the car immediately ran better with a smoother idle and better throttle response although it did, unsurprisingly eventually throw up two faults related to low signal from the MAF and the temperature sensor.

This seems to confirm that the MAF is faulty.

I removed the plastic clip around the top and can only see one sprung metal clip at the back holding the unit down but despite pushing this back the unit is not coming out, are there more fixings to release?

Thanks as ever.
 
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Allybally

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Brute force eventually got mine out,think it had expanded through heat. It should have 2 metal clips on it tho!
 
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DSM10000

DSM10000

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Brute force eventually got mine out,think it had expanded through heat. It should have 2 metal clips on it tho!

Thank you.

Just returned from a weekend away and have had another look. There is a plastic clip at the top (removed)and towards the back and lower down is a metal clip that appears to need to be pushed back.I cannot see any other clips but they may be behind pipes etc.

The whole elbow joining the MAF to the throttle body is now moving after releasing both of the above but not coming out completely nor is the MAF separating from the elbow as I assume it does?

I have the Haynes manual somewhere, I will see if they have any pictures that show the retaining clips more clearly. It seems a simple thing to remove but I am loathe to pull any more firmly at the moment.
 

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