2003 Monte Carlo SS check engine light flashing Pleas Help!

Hi. My 2003 MC SS has been acting up, the check engine light starts flashing at me and the car starts shaking when I turn the AC/Heat on. I have no idea what is going on. I know nothing about cars and before I take this to a mechanic, could someone tell me what might be the issue, I do not want to go somewhere and get totally ripped off.

Thanks

There is probably a misfire code set, could be a general code, or a cylinder specific code. May be caused by several things. Plugs, wires, coil(s), ect...,with the a/c on, its adding a load and making it worse. Need to have the codes checked.

My friend just ran the codes and we got some cruise control codes and a solid misfire on the 5th cylinder but he has no idea what it is. Do you have any ideas for me?

Not sure on the cruise codes. With the #5 misfire, could have a bad plug, wire, coil, or even a burned valve in the head (least likley, but possible). Start with the plugs. espically if they have not been replace in a while, you can even swap plug and/or wire to another cylinder and see if the misfire moves. If its been awhile since the pluge and wires were replaced, I would just do that and see what happens.