95 mustag gt rough idle

I am kinda new at this I have spent countless hours readying forum stuff but I have not come across my problem yet.... I have a week idle and when the a/c is on it is even worse.... If it just sits in park and idles the amp meter on the dash starts to head toward the 8.... ?
If the car is in drive it has a normal idle... I am so lost trying not to spent tons of money and don't want to change a million of other parts to figure out what is going on....
Any thoughts on what to do next ?

I have a 95 gt w/aode that is mostly stock....
I added a mac aftercat exhaust, mac offroad x pipe,( after I put this on the check engine light came on not when I start the car but after a few miles down the road) I replace these items trying to get the check engine light to go out....
msd coil, cap, rotor plugwires and new plugs ngk


no luck.......


please help.....?

I also have a cheap cold air intake I put on the car.... would this have caused any of my problems....?

is there a cheap way to pull the codes...
would a auto parts store have a cheap code reader or is that something i would need to have a mechanic do?

thank you very much man I will probably go and purchase one at the auto parts store that way I will have this in case this happens again....

jmills