[Tatsfield]

Not that I've tried it on car components but you can buy oven cleaner that cleans carbonised oven parts by putting them in a supplied plastic bag, adding the chemical and leaving it soak for hours. Take it out, rinse in water and throw the bag and waste chemical away. Works a treat on very very carbonised oven parts and you don't run all the risks that you do with caustic sprays or cloths etc.