My Hyundai XG has about 40,000 miles on it, full tank of gas but today while driving it feels like the engine is not getting enough gas - when I accelerate the malfunction light for exhaust gas lights up and goes off. My husband power washed my engine yesterday and put Armour All on the engine - could he have harmed something and caused engine trouble today ?

It's certainly possible that water left over from the engine cleaning is the culprit. There are a lot of electrical connectors and components under the hood, and they don't like to be wet. The fact that the car started this morning and runs is good - you may find that after a day of driving the heat of the engine drives off any excess moisture and the problem will clear up on its own. As for using Armour All on the engine - that's probably not the problem unless he used it on sensitive electrical components, such as spark plug wires or spark plug boots.

As a side note, I think using Armour All is a bad, bad idea. Yes it makes things look all shiny, but it has been known to harm plastics by pulling out the plasticizers, which can cause plastic parts to prematurely age and crack. It's probably worse in the hot engine compartment. It's especially bad to use on tires, as it pulls the waxes out of the rubber compound, which makes the rubber less pliable and can cause cracking. There are much better products out there for cleaning and treating plastic and rubber - see for example
Car Care Specialties, Inc. - Your Source For Quality Car Care Products, How-To Articles and Product Evaluations. (http://www.carcareonline.com/viewarticle.aspx?art=4) and
Car Care Specialties, Inc. - Your Source For Quality Car Care Products, How-To Articles and Product Evaluations. (http://www.carcareonline.com/viewarticle.aspx?art=12)

Thanks SO MUCH for your answer and I hope you're right. Have a GREAT day !
:)