Mercedes-Benz W201 vacuum leak and the injection rubber boot
W201 idle fluctuates, could the injection rubber boot be the cause?
Yes. The rubber boot under the injection unit cracks with age and lets extra air into the engine. It upsets the idle and can stall the engine. The boot moving up and down shows that it has a hole.
How is the rubber boot attached and how is it repaired?
The boot is held by a clamp at the bottom end in the throttle body housing and at the top end in the airflow meter. Small cracks can be patched temporarily with putty, but the boot should be replaced with a new one. For replacement, the air mass meter and fuel distributor assembly is removed: three nuts and one clamp.
What else is checked if a vacuum leak is suspected?
Check the tightness of the clamp at the ends of the boot and the condition of all the air hoses. After the air cleaner has been removed, the hose going to the valve cover and the idle control valve can be left kinked or broken, making the engine run badly. Replace a damaged hose with an intact one.