Iz Haynesa:
Engine idles erratically:
- Air filter element clogged
- Vacuum leak at the carburettor/throttle body.
- Inlet manifold or associated hoses - petrol models
- Worn, faulty or incorrectly-gapped spark plugs - petrol models .
- Uneven or low cylinder compressions
- Camshaft lobes worn
- Timing belt incorrectly tensioned
- Blocked carburettor jet(s) or internal passages - carburettor petrol models
- Blocked injector/fuel injection system fault - fuel-injected petrol models
- Faulty injector(s) - Diesel models