I was going to reccommend Kenco Shift-It.
Worked a treat on all my seats and headlining.
Spray on, wipe with a damp cloth, then blot with a dry cloth to remove excess moisture.
Gentle enough to use on fabric, and strong enough to clean oil, grease and dirt scum from the engine bay.
(Not sure if I'd want to put carpet cleaner in the engine bay?)