Carbon deposits - accelerator housing

[alex b]

Took the wife's A class in for the airmass sensor to be changed under warranty, and I was told by the service manager that when the diagnosed the airmass problem they noticed there was a "carbon build-up" on the accelerator housing that could also be causing the lumpy idle/acceleration.

The cost to clean this deposit 60-90 minutes labour @ £102+vat.

Is the carbon deposit thing BS, or is it a real problem?

Thanks

Alex

[trickywoo]

So much of that sounds like BS! I know a bit about cars but can't imagine what an "accelerator housing" is or how it may come to have carbon on it.

The only way you are going to get carbon on anything is from exhaust gasses. So if its getting onto some kind of "housing" that would say exhaust leak to me. As for 60-90 mins labour to clean it, hes having a laugh.

Diagnosing the AMF would have involved pluging the ecu into a computer can't imagine there being much carbon around that.

[Parrot of Doom]

If its got an EGR system, it'll have a carbon buildup. They all do. Mine has huge thick deposits of the stuff, which I've cleaned off in the past.

You can clean it off yourself, carb cleaner spray will do it. Don't get any on the MAF. If you want to clean the MAF, used a tin of isopropyl alcohol spray.

[alex b]

Where should I look on an A-class?

[silverback mike]

It sounds about right.

And dead easy to clean yourself. All you need is a screwdriver, a can of carb cleaner and a toothbrush and a rag.

Dismantle the airbox assembly (where airfilter is), so you can see the throttle body.Give it a big squirt of carb cleaner into the butterfly mouth whilst engine turned off, dont' be afraid of opening the butterfly by pushing a finger in there. You will see the carbon coming off, keep squirting and cleaning until it's nice and shiny, squirt some more down there for good measure.

Start the car, be advised though it will sound like a bag of spanners for a bit, and smoke like a jalopy, this is all the crap burning off the intake, and inlet manifold and coming out of the exhaust pipe, whilst its running raise the revs and get some more carb cleaner in there, the revs will drop, it'll cough a bit but thats a bit like it clearing it's throat.

Should be lovely and clean now, refit is the reverse of removal to coin a phrase from haynes and there you go.

I cleaned silverback seniors C200 throttle body when I serviced it, he was absolutely amazed at how smooth the throttle power delivery was, it wasn't that dirty either.

As for £102 , a can of carb cleaner is about a fiver, toothbrush - well, use the wifes there we go.

Job's a good un.

hth
Mike.


PS, This is the butterfly throttle body - it will look similar, if not the same..
http://i3.ebayimg.com/02/i/06/fa/38/c

Not the best picture, but forget the bit that says "bmc", that's a performance filter, it will be under the big black box, so whip that off and the pipes to the air intake (you can see the where the original should be on this just to the right hand side front of the radiator) and the off you go.
www.atb-tuning.de/shop/artikelBilder/CDA10A-bild.jpg

Hope that helps a bit...

Edited by silverback mike on Sunday 11th February 00:57

[alex b]

Thanks Mike

Will give it a go next weekend.

[jith]

Mike and Alex, can I just add in a wee note of caution there.
Pulling all the crap that will be dislodged by the cleaner through the engine is a decidedly bad idea, as it could damage the cat by partially choking the intake side of the matrix.
The channels in a cat are extremely small and do not take kindly to anything oil based, carbon solids, or thick, oily substances.
Although it's a bit more work, better to remove the throttle body and associated parts and clean them on the bench safely and refit them clean; no crap in the engine, and problem solved.
Incidentally, on many cars with this type of breather system, not just Mercs, the breather hoses themselves become restricted and even blocked causing increased oil consumption, so it's worth checking these out also and cleaning them.