1. Faulty spark plugs or electrode gap set incorrectly (see «Spark plugs - replacement» or «1.6i engine spark plugs - replacement»).
2. Faulty high voltage wires (see «High voltage wires - check and replacement»).
3. Leaky vacuum hose connections (check the tightness of the fit on the fittings).
4. Faulty ignition coil (see «Ignition coils - check and replacement» or «1.6i engine ignition coil - check and replace»).
5. Insufficient compression in the engine cylinders (see «Compression in the engine cylinders - check»).
6. Faulty fuel injectors (see «Nozzles - check and replacement»).