Cold-start valve and thermo-time switch provide a short enrichment pulse on cold starts. Stuck open floods; no pulse makes hard cold starts.
Related: K-Jetronic, WUR.
Function
Switch allows a brief valve pulse when cold; pulse should end as temperature rises. Wiring and power integrity count.
Hard start vs flooding
No pulse: valve/switch/wiring. Stuck commanding open: rich smell, wet plugs, miserable warm starts. Clear floods safely then fix the cause.
Testing
Meter power/ground, switch versus temperature, valve operation per service practice. A digital multimeter helps the electrical half.
Common mistakes
Skipping a cold and hot test drive, trusting verbal history without invoices, replacing parts before measuring, and ignoring rust while chasing mechanical gremlins. Another classic mistake is using photos from a different market or year as if they were a parts catalog.
When to stop DIY
Stop when you lack the gauge, puller, or safe support the job needs — or when the first repair did not change the symptom. A second identical guess rarely helps. Pay for diagnosis with a specialist who sees R107s regularly.
Practical takeaway
Verify several real cold mornings after parts — not one heated-bay start.
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Verify procedures against the factory manual for your engine and chassis. I do not invent details about a specific personal car here — use your plates, your invoices, and your measured symptoms.
Shop notes and paperwork
Keep invoices, pressure readings, part numbers, and dated photos of the area before and after work. The next owner — or future you — will ask what was actually done. Verbal “we took care of it” evaporates at sale time.
Safety and scope
Use jack stands on solid ground, relieve fuel/coolant pressure before opening systems, and disconnect the battery when the procedure calls for it. If a step needs a specialty tool you do not own, rent it or hire it — improvising with the wrong lever is how fasteners and fingers break.
If this topic intersects fuel, rust, or safety systems, fix the safety and leak paths before cosmetic or convenience items. That order saves money twice.
