Personally I'd stay away from armorall. Autopia forums have a thread about it, and the last post says a lot. A guy that I work with is in to classic cars he and his friends swear armor all ruins your dash and plastic components over time.
heres the link to autopia.
Armor All bad??? - Autopia.org
I just use the same auto shampoo/water mix i use to wash the exterior of my car on a microfiber cloth. Then I follow up with a wet microfiber cloth. It keeps the engine clean, and I do it every other time I wash my car. I get any small spots with Adam's detailing spray that I happen to miss.