W203 C180K Sports Coupe Idling speed question

[darkforce82]

Hi, I just bought this car. I found when the engine is fully heated up, the idling speed is high at around 1200 rev/min. And falls gradually to around 900 rev/min if I idle the car for 1-2min.

If I switch the air-con on, the idling speed will fall to 800 rev/min, but turn it off will send the speed to 1200 again.

No fault reported by the on-board computer.

I have never owned a car with Kompressor, and don't know if this is some "distinct" characteristic of this type of engine.

Will be appreciate if anyone can point me to the right direction.

 

[Kerja]

Well, I had the same issue on the Smart Fortwo, but nothing similar on parents W209 200k
Might been the "pre-heating oil" issue

 

[darkforce82]

Just did a bit of test:

When the engine is heated up, idling at 1200 rev/min, I switch the engine off, wait 30 sec, then switch it on, it will be idling at 800 rev/min for about 2-3 mins before it shoot up to 1200 rev/min.

This makes me feel that the problem is because of some fluid, i.e. when switch the engine off, the fluid will flow back to its container and when switch the engine on, the fluid will take some time to flow into the circulation system. And when the fluid is in circulation the engine will be idling at a high speed.

Does this ring a bell for anyone?

 

[Kerja]

well, the only thing I can think of, is a throttle body, that needs cleaning. It might fix the problem.

 

[darkforce82]

How much will it normally cost to get the throttle body clean at a garage? Or is it easy to DIY?

 

[Kerja]

Well, I was doing it on my smart on my own.

Here's the guide for the smart, but it must bee similar to the merc as well

Evilution - Smart Car Encyclopaedia

when removed, give it a clean with something like that: Wynns Carburettor Cleaner 500ml from Halfords Price £5.49

It might solve the problem.

For me for the first time, it took about an hour to remove it, clean and place it back.

 

[darkforce82]

Excellent, thanks, I shall open the bonnet and see if I can locate the throttle body.

 

[bones2008]

My C230k doesn't act like that, and the Kompressor would't affect the idle.

It does sound like a throttle body problem, so I'd try cleaning that first.

 

[lynall]

Item 200 Êàòàëîã

Try not to unplug the electrics from the throttle body when you clean it as i did when i did mine as it took a while for the throttle to relearn and i had high idle etc same as you have now.

Unbolt body from manifold ( i have cleaned some in situ before) Aerosol cleaner and an old toothbrush, spray in clean with brush, manually open throttle and clean around the edges of the flap, rinse off with more cleaner allow to dry done.

Some are a doddle to clean wifes old bmw e36 springs to mind, mine is harder as its at the back of the engine v.


Lynall

 

[darkforce82]

Enn, thanks for all these suggests.

I would like to give a bit more update. Today I drove the car from London to Canterbury and back, 120miles in total, reached 90MPH on M2.

When I got Canterbury, stop the car and let it idling, the engine rev from 1100 to 1600 back and forth, makes me feel very uncomfortable.

Also, the fuel consumption seems to be normal, I did 41.8MPG, not too bad.

I bought the car from Cargiant two weeks ago, I called them and they said they would repair for feel. I guess I probably should take the car to them first and give it a go hope they can fix the problem with good faith.

 

[Kerja]

if they'll repair it for free, just take it down to them.

But ask them, what have they done, to fix it. If it's throttle body, You have nothing to worry about. Do you feel any excess vibrations as well, when the car is idling (normally idling) because it might be the injectors that are dead.

 

[darkforce82]

In terms of vibration, I would say it is quite normal. Compare to the Golf and Mini I drove before, I can say this Merc is on the smoother side. In high speed it is quieter.

The car has done 63K miles so far, any idea how long an injector on a Merc normally last?

 

[Kerja]

well, they last plenty. but it depends on the petrol which was used and is used now.

 

[lynall]

Wont be an injector problem , i had mine checked a while ago and the bloke said we dont see merc petrol injectors ever.



Lynall

 

[darkforce82]

Got update from Cargiant, they said this is a problem with Inlet Manifold and they will replace it with spares.

Have anyone experienced problem wth Inlet Manifold, is throttle body mentioned above part of the Inlet Manifold? Is this a big problem or not?

 

[NormanC]

To me it sounds like an air leak between the airflow sensor and the engine. This could be a cracked inlet manifold which the dealer says they'll replace.

Many years ago I had a Vauxhall Carlton which suddenly started blipping the throttle with no-one in the car!! Revs would blip from 850 to 2000 just like a boy racer. Found a loose jubilee clip on the pipe between the airflow sensor and the manifold. Tightened this and the problem went away.

 

[Noodle-Pulp]

Just for info I've had a 2003 C200 coupe and now I have a 2007 C230 coupe - neither show any of the symptoms you're describing.
So it's certainly not "normal", but you knew that already.
Was this fixed in the end, and what precisely was the fault?

 

[Adam230K]

I had something like this on my 230K and it turned out to be the throttle spring. But i dont know if your engine has one.

 

[markjay]

Just to say that my C180 Kompressor idles steadily at 600 rpm when warm, so I guess this is what you should expect to see once the problem is sorted.