W202 C230K High Idle Problem

[DITTRICH]

When started at ambient temperate "from cold" the revs initially rise to 1,400ish and then stick persistently at 1,200 for a minute or two and thereafter gradually over the next minute or two reduce to around 800.

I think this is wrong. Why?

Because before around 2 years ago, the engine would immediately settle down at 700 - 800 after the initial rise to 1,400.

The car is 1999 vintage - facelift - and has done 108,000 miles. None of the various sensors have been replaced. The garage did instal some new "throttle slide actuator" or some such thing £525+VAT to see if it was the issue - it wasn't. I started the car at the garage today in their presence and it still sticks at 1,200 even at 24.5 deg c ambient temperature from cold.

I was told that this "throttle..." thingie controls the idle speed and takes its commands from the ECU. The ECU gets inputs from all over the place including:-

1 Lambda sensor in the exhaust
2 Mass airflow sensor in the air intake pipe
3 engine temperature sensor (radiator? engine?)
4 crankshaft position sensor?
Is this list complete? Are some of the above irrelevent?

Given that the behaviour seems to disappear after 3 minutes from cold, something is obviously working better as it warms up. The question is WHAT?

The techs have had the car hooked up to diagnostics and looked at the startup characteristics from cold but everything is "in spec" they say. However, I know that sensors fail over time and slowly go "out of spec".

I know very little about cars but I do know that £525+VAT is alot of money.
All advice from man on't'internet gratefully received.
I'm picking the car up today at 6pm for the weekend and its going back on Monday. Only difference, this time I hope to tell them what to do, rather than let them tinker by themselves.

Thanks

Les

 

[gina2201]

I may be way off the mark but thought I'd reply anyway.

I also had a w202 C230k which used to idle at above 1000rpm. When it went in for a service, I asked them to have a look and they said the "throttle return spring" was missing (costing 70p).

I would have had it done there and then only they had to order it in so I never actually got it done before I sold the car.

My current car, (Golg GTI) 8 times out of 10 will idle too high at about 1500rpm if I let it, or if I dip the clutch and let go it will shoot right up to 2-2500 then drop down to 1500rpm. I have to engage a gear and let the clutch bite for the revs to drop then it will settle and idle at 800 rpm nicely. I think my throttle cable is getting stuck/sticky so am going to replace that shortly.

On my E220 Coupe I had to clean out the throttle body with carb cleaner and hey presto, the random crazy idling stopped (and this car used to dip it's revs so much it had cut out on me whilst on a roundabout and on corners-not ideal).

These are obviously very simple solutions and maybe unrelated, but maybe worth a squirt of carb cleaner or wd40 on the throttle cable anyway? Wouldn't do any harm.

Good Luck in a diagnosis, I know I prefer to try the free things first!

 

[Dieselman]

I would've thought with a new throttle body it had had a new throttle return spring, but a worthy suggestion and worth checking .
Another thought is that coolant sensor reporting the wrong value so holding the ECU on 'choke' as it were.
Worth checking for a vacuum leak as well as this will allow th eengine to idle high but would normally continue after it is fully warm.

 

[Nasco12]

Did you find a solution to this? I have more or less the same symptoms. I find that if I shift into Drive at high revs I get a rather disturbing ker-lunk sound with associated jerk forward but if I wait for the revs to drop it's altogether much smoother and less alarming.

 

[Liloff]

Reviving an old topic.
I drive 111.944 engine CLK W208 200 Kompressor.
My problem is that sometimes, quite rarely though... When I start the engine hot, it keeps the revs high. I rev the engine, it keeps them high and slowly, but i mean veeery slowly goes back to idle.
When i restart the engine, the issue is sorted.
It doesn't feel like a mechanical issue. I read the story about the 70p spring that went missing, but definitely not the case.
I have cleaned the throttle body. There is a nice topic about that in our mbclub.bg forum, however this issue slightly pisses me off.

Any other clues?
(Could it be vacuum line... the easiest thing is to wrap all the vacuum lines in thermo-shrinkable tube and see how it acts...)

 

[mauricekan]

any update with this problem?

I have similar issue which I couldn't fix! please help!

 

[t-dawg1]

I had that same issue once on my w202 1999. Turned out to be a faulty MAF.Mass airflow meter. Got a new one cheap online and my car was back to normal. I'm 99% certain that's what ur problem is so I wouldn't waster time and money looking at other areas