W202 C200 exhibits rough operation and failure to idle during the cold start warm-up phase.

[norbury.brook]

Greetings, everyone.
I apologise if this topic has been already addressed:
I just purchased a 1998 W202 C200 (m111 engine) for my son as his first automobile for his birthday, aiming to instill brand loyalty early, so he would not sell my old Mercedes after my passing. During cold start, it operates very unevenly and fails to maintain idle. It is necessary to manipulate the throttle to achieve approximately 1500 rpm to maintain operation until the engine temperature reaches around 60 degrees Celsius, at which point it operates smoothly. However, at maximum throttle during kickdown to first gear on the open road, it exhibits roughness and intermittent clearing, contingent upon the precise throttle position within the 75-100% range (ideally, he will remain unaware of this full throttle issue and will not reach that state). However, I saw this during the test drive while inspecting it, which led me to consider the throttle body potentiometer or a related component.
I am uncertain if this is related to the cold start warm-up defect mentioned before, but this is the issue I am more concerned about resolving before I hand it over to him.
It is a New Zealand new specification vehicle, hence it will possess the same emissions equipment as a UK new model, since I have seen that they generally share the same specifications.
Best wishes, and I hope the weather is beginning to improve in Britain.
Thank you.

[BENZE220AMG]

Test the system with the air mass sensor unplugged; does this result in smoother operation?

[norbury.brook]

I will attempt later and return to you. Thank you, friend.

[SD1too]

You are a commendable parent for purchasing a Mercedes for your kid.
It signifies that you are concerned about your kid.

[coolguy]

Is it permissible to contact AA/RAC if one has breakdown coverage?

[norbury.brook]

Indeed, he enjoys it as well! He was utterly astonished. The W202 models are very robust. Front and side airbags are present, the air conditioning effectively clears the glass, and the A-pillars on the W202 are rather small, resulting in minimal blind spots. Additionally, it implies that he will experience my W202 C36, therefore increasing the likelihood of retaining it within the family in the future. Thus, not entirely altruistic motivations!
He has just turned 16, therefore qualifying for junior AA membership (there is no RAC in New Zealand).
However, I do not believe they provide a solution to rectifying this flaw.

[SD1too]

A new Bosch air mass sensor would likely suffice.
This component is renowned for its propensity to malfunction.
Purchasing from a dealership is expensive; get authentic components from an auto parts shop for much less.

[norbury.brook]

Understood. Thank you, SD1too. I attempted to disconnect the device last night, as recommended by Dodpops, to see whether it would ameliorate the problem. However, the cold start issue persisted, although I speculate there may have been a marginal improvement, maybe a product of my wishful thinking. However, it still would not maintain idle without raising the RPMs to around 1200-1500.
Should I have obtained a more conclusive outcome by disconnecting it and attempting a cold start?
My gratitude extends to both of you.

[SD1too]

Has this automobile been properly maintained?

Are the spark plugs and wires in satisfactory condition?
Are coil packs acceptable?

Are there any suction leaks from deteriorated hoses in the intake system?

A multitude of issues might arise with an ageing vehicle.

[Psychil]

I would connect it for diagnostic analysis.

If it is performing poorly, identifying the problem should be straightforward; otherwise, you risk creating further complications, and indiscriminate component replacement may become costly.

[neilrr010]

Did the replacement of the Air Mass Sensor resolve the issue?