I have a 2002 Ford Mustang 3.8 v6 and just recently I noticed my car was idling very rough

Even more when in gear though. I didn't think anything of it until i drove it and the SES light started blinking so I felt that was odd. My car idles so hard I think it's going to stall but it never does. It doesn't have much power expessially when going up hills. I looked it over and found a air hose unplugged so I plugged it back in but it still does it. Is there anything I can do?

Take it to a shop. Its an old Ford, thats your first problem.

It's probably not firing on all cylinders. I'd recommend cleaning or replacing the spark plugs and then checking each distributor lead for a strong spark at each spark plug, but my guess is that you don't have the knowledge or skills to do these things.

Hi so what do you expect from a 15 years old car might be the issue.

Can be anything from bad plug/lead loose connection etc to low fuel pressure /air leaks and so on. A simple skilled mechanic check over at a garage is simplest way to proceed. Get a price to check car over and a quote for any repairs needed. With luck a simple issue. Do not be tempted to carry on driving with this issues as any damage can be made far worse!