99 CLK200 Massive dead spot at low revs

[Mikesmerc]

Hello all, my clk has developed a nasty dead spot at low revs, will not accelerate until the revs slowly pick up, only then she preforms how she should. Replaced the the plugs last night with no improvment. Did notice the plug tips are more white than sandy brown in color.
Any ideas?
Mike

 

[tom7035]

Sign of a lean mixture. Check all your vacuum connections are sound and for a possible inlet manifold leak.
After that, it's down to an electronic gismo of which I know extremely little I'm afraid. Someone else will offer advice in this respect.

 

[jberks]

The first suspect would be the MAF sensor. Try unplugging it and see if it makes any difference. You can also try cleaning it as per the sticky post or just replace it and be done with it.

 

[OmniCognateNeutronRangler]

Always seems to be the MAF sensor. It's the Benz equivalent of "the butler did it".

Must say I had one die on my Audi too and that had similar sounding symptoms. At the advice of the Audi Dealer in Portsmouth (when the car completely died on the way home after them looking at it) I disconnected it and the car went like a rocket. Apparently it does no real harm just messes up the mixture a bit if you disconnect it (I'm not technical enough to know if that's true or not but it did no apparant harm to the Audi and I drove it with the sensor disconnected for nearly 2 weeks whilst the garage got a new sensor).

 

[Mikesmerc]

Thanks for the help guys, will have a go at the weekend.
Rgds
Mike

 

[Mikesmerc]

Well, I had a look the MAF sensor tonight as she backfired tonight when accelerating from low revs. I must say it all looks very clean, even the tubing, no oily deposits and the air filter looks new. So I reassembled the hoses etc and had a good look around the inlet manifold for any loose vacuum hoses/leaks and all looks well. I the disconnected the MAF sensor and went for a spin, big improvment on acceleration no real flat spot at all, seems to power up smoothly enough. With this I assume its a faulty MAF sensor but will try cleaning it with Isopropyl Alcohol , I presume I can spray this on to the element directly without doing any harm to it???. Next question, where should I look to buy this stuff?.
Thanks everyone
Mike

 

[veedweeb]

will try cleaning it with Isopropyl Alcohol , I presume I can spray this on to the element directly without doing any harm to it???. Next question, where should I look to buy this stuff?.
Thanks everyone
Mike

You can spray it directly on the sensor. Use loads as it can't do any harm. HOWEVER, you MUST let it dry naturally - don't blow on it, wipe it with anything or touch it in any way.

You can buy it from Maplin electronics - it's about a fiver for a big aerosol of it.

 

[tom7035]

Can get it also from independent chemists. For some strange reason I find B---s don't keep it.

 

[Mikesmerc]

Thanks VW that helps alot, will let you know how I get on.
Cheers
Mike

 

[Mikesmerc]

Cheers Tom, missed your post by seconds by the looks of it.

 

[Mikesmerc]

No luck with cleaning the sensor Im afraid but was worth a go. Think I will do a swap with my brothers 98 C180 if the same just to confirm. Is there any lecky test I can do with this and how much roughly is a new one?
Thanks
Mike

 

[jberks]

Worth a try swapping - though I believe you've already proven the fault by disconnecting. They used to be expensive (mine was over £200 from memory)though I believe the prices have come down considerably recently so it's worth a call to the dealer. Also try Euro car parts and then finally, you may be able to just buy the insert and swap them yourself (substantial saving) so give your local Bosch agent a call before you decide.

 

[television]

Well, I had a look the MAF sensor tonight as she backfired tonight when accelerating from low revs. I must say it all looks very clean, even the tubing, no oily deposits and the air filter looks new. So I reassembled the hoses etc and had a good look around the inlet manifold for any loose vacuum hoses/leaks and all looks well. I the disconnected the MAF sensor and went for a spin, big improvment on acceleration no real flat spot at all, seems to power up smoothly enough. With this I assume its a faulty MAF sensor but will try cleaning it with Isopropyl Alcohol , I presume I can spray this on to the element directly without doing any harm to it???. Next question, where should I look to buy this stuff?.
Thanks everyone
Mike

There are many switch cleaners as used in the electroncs industry, you need the cleaning type and not the lubrcating one. available from CPC,Farnell and maplins. What the MAF does is to set the mixture to suit the ambiant temperture.

Malcolm

 

[124coupe]

Running with the MAF disconnected for a while just means the car runs on a default map rather than finely adjusted to the air temp/car height above sea level. The ECU will still respond to the O2 sensor and so the mixture will not be far out.

(running with the "bad" MAF is far worse as it is clearly still outputting a signal which the ECU believes is in a viable range and so is trying to tweak fuelling to match the wrong airflow figures - usually the result is to run VERY lean).

They are often on Ebay, otherwise Eurocarparts, GSF, KMS stock them. My cheapest was Bosch locally, but they could only work off the insert part number which, on my car, required the insert to be removed (2 security torx screws) as the number is hidden on the side of the insert (Bosch did not list the "Bosch" part number on the outer unit).

 

[television]

. My cheapest was Bosch locally, but they could only work off the insert part number which, on my car, required the insert to be removed (2 security torx screws) as the number is hidden on the side of the insert (Bosch did not list the "Bosch" part number on the outer unit).

Yes this is correct, the filter element is made by Bosch, but the plastic housing is made by MB. All Bosch agents will supply the filter element on its own, and this must be the best way to buy one, it will always be a good unit and up to date.

malcolm

 

[Mikesmerc]

Sorry for not getting back earlier, up the walls, havent even had time to swap it. Over the next few days I will price around the various options and let ye know how I get on. Will disconnect it for a while, bit dangerous as it is, especially at juntions when you need to give it some welly.
Thanks
Mike

 

[Mikesmerc]

Picked up a new sensor today, 111 euros. turned out to be a Pierburg part rather than a Bosch. Now to find a torx to take off the anti-tamper screws.
Mike

 

[124coupe]

Halfords have them both mounted individually as screwdrivers and as separate bits.

Make sure you buy "security torx" assuming yours have the pin in the middle.

 

[jimsinessex]

I bought the Halford's security Torx bits and they wouldn't fit the screws on the MAF sensor. If you find a set that fits I would be interested to know the make and where you got them.

My car is a 1999 CLK 230K but the MAF sensor was renewed with a MB one complete with casing in 2004. It is this one that the the Halford's security bits won't fit, the centre pin is fatter and the splines look quite "beefy" with squared off tips.

To summarise:- are there two different types of security Torx screws?

Jim

 

[124coupe]

Torx is a standard so they must be something else. Mine came as part of a 3/8 socket set and have fitted everything so far.