The early Mk1 and Mk2 GTI run CIS (K-Jetronic / KE-Jetronic) — Bosch mechanical continuous fuel injection, not an ECU-and-injectors system. Reliable when understood, but alien if you grew up on OBD.
How it works: an air-flow sensor plate lifts with intake air and mechanically meters fuel through a fuel distributor to injectors that spray continuously. KE-Jetronic adds electronic trim.
Common issues:
- Hard starting / poor running from a worn or sticking fuel distributor or control-pressure (warm-up) regulator.
- Vacuum leaks — the system is very sensitive to unmetered air.
- A worn air-plate pivot or dirty injectors.
Troubleshooting:
- Check system, control and rest pressure with a CIS gauge set — that's the diagnostic language here, not fault codes.
- Fix every vacuum leak first.
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