100% mechanical issue.
Idle during warm-up is controlled by THERMOSTATIC additional air valve.
There are many hoses under the intake to distribute the air to the intake.

Idle is adjusted by large plastic screw.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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44 years foreign automotive repair
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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