91 Monty....daughter has been driving it for months and I just now found out maint reqd light is on. Engine idles fine and drives good but stumbles when a quick acceleration is needed. Leaky valve covers....shes says it shifts funny when AC is on. I just found this out because she wore rear drum down to the metal (this should show her resp. level). It only has NINETY thousand original miles. Soon as I can find her another car I'm taking it back!!!! Well guess what I'm asking is for some leads on what sets that light off and how do I check the codes. I'm new to the six cylinder and bad with the search thingie so I apologize for that. Thanks for the help.

cjm