I have Toyota Duet 2002, with twin cam engine, manual transmission. As starting the engine, the rpm reaches to 2100, sudden falls below 1000 rpm and keeps on doing up and down and never stay in control. As I press accelerator the rpm falls below 1000 rpm and the engine goes off. When convert on CNG the rpm gets stable on 1000 but the car doesn’t gets in instant pick, also vibrates while pickup.
Some mechanics say it could be due several reasons like: car sensors/computer card / throttle body / fuel injectors / fuel pump. I have also changed the clutch and pressure plates but the vibration thing is still the same.
Can anybody suggest what to do where to go? What is the best solution?