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The W202 C200 has harsh running and fails to idle during the cold start warm up phase.

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Greetings, everyone.
Apologies if this topic has already been addressed:
I just purchased a 1998 W202 C200 with a m111 engine as a first automobile for my son's birthday. My intention is to introduce him to the brand at an early age, with the goal that he would not simply sell my old Mercedes cars once I pass away. During the first start when the engine is cold, it operates with significant roughness and fails to maintain a stable idle. To maintain the engine's operation, you need to manipulate the throttle and set it to approximately 1500 rpm until the engine temperature reaches around 60 degrees Celsius. At this point, the engine runs smoothly, except when using kickdown to shift to first gear at high speeds on the open road. In this scenario, the engine may run unevenly and sporadically clear up depending on the specific throttle position within the 75-100% throttle range. It is preferable that this full throttle issue goes unnoticed and is never encountered. However, during the test drive, I saw a particular issue that caught my attention, leading me to speculate that it may be related to the throttle body potentiometer or a similar component.
Therefore, I am uncertain whether this issue is related to the problem that occurs during the warm-up phase of a cold start. However, I am more concerned in resolving this particular fault before I hand it over to him.
The automobile is a New Zealand model, which means it will have the same emissions equipment as a new car in the UK. I have observed that they all appear to have the same specifications.
Greetings and I hope the weather is becoming more pleasant in Blighty.
Thank you.

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Indeed, he too has a strong affection for it! He was quite astonished. The W202 versions are still quite durable and reliable. The vehicle is equipped with front and side airbags, and the air conditioning system effectively clears the glass. Additionally, the W202 model has very small A pillars, resulting in minimal blind spots. Additionally, this will allow him to develop an appreciation for my W202 C36, increasing the likelihood that he will continue to own it in the future. Therefore, the motivations are not only driven by selflessness.
Indeed, he has just reached the age of 16 and is now eligible for a junior AA membership, since there is no RAC equivalent in New Zealand.
However, I do not believe that they are the solution to rectifying this flaw 🙂

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Installing a new Bosch air mass sensor is likely to resolve the issue.
This component is prone to failure.
Purchasing from a dealership might be expensive, but you can get authentic products at a far lower price by buying from an autoparts shop.

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Understood. Thank you, markjay. I followed Dodpops' suggestion and unplugged it last night to see if it would resolve the issue. However, the problem persisted when I started it again when it was cold. I did see a tiny improvement, but I'm not really sure whether it was real or just my hopeful imagination. However, the engine would not maintain a steady idle speed until I increased the revolutions per minute (rpm) to a range of about 1200-1500rpm.
Would I have obtained a more conclusive outcome by disconnecting it and attempting a cold start?
I appreciate the contributions from both of you.

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Has this automobile been properly maintained?

Are the spark plugs and wires in good condition?
Are the coil packs functioning properly?

Are there any vacuum leaks caused by deteriorated hoses in the intake system?

Numerous malfunctions may occur in an aged vehicle.

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I would connect it to a power source in order to do diagnostic tests.

If the performance is already subpar, it should not be difficult to pinpoint the underlying issue. Otherwise, there is a risk of exacerbating the problem by adding more complications or variables, which may result in costly shotgun component replacements.

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