🚗 Classic Fault — Mercedes-Benz W115 (1968–1976)
Mixture screw O-ring deteriorated causing lean idle
💰 Estimated Repair Cost
$2 – $8 USD
Parts and labour estimate
🔧 Tools Required
Mixture screw tool, pick tool
📋 Overview
The small O-ring sealing the idle mixture screw deteriorates with age and fuel exposure. Air leaks past the screw, creating an uncontrollable lean mixture at idle regardless of mixture adjustment position.
🩺 Symptoms
- Idle cannot be made rich enough
- screw position has no effect
- very lean idle
- high idle speed
🔍 Possible Causes
- Deteriorated mixture screw O-ring
- damaged mixture screw taper
🛠️ Diagnosis Steps
Remove mixture screw. Inspect O-ring — should be soft and round. Hard, flat, or cracked O-rings confirm issue.
✅ Most Confirmed Fix
Replace mixture screw O-ring with Viton type. Readjust mixture.
90% of users confirm this fix worked (44 reports)
🏷️ Parts Needed
Mixture screw O-ring (1.5x1mm Viton)
🔗 Other Mercedes-Benz W115 Faults
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