Erratic idle at stoplights

I can think of several things that would cause the symptoms you describe. You didn't say whether you had the problem before you replaced the intake gaskets. I assume you replaced the gaskets because you had the problem at that time. If you got the problem after you replaced the gaskets, then I suspect a vacuum leak and you need to recheck your work. Either way, I'd check for vacuum leaks into the intake, using a smoke machine or propane or carb spray, at least. A good diagnostic technician would have a smoke machine. You don't say whether the check engine light is on, but if it is, there are data and diagnostic codes stored that would probably lead you to the problem. A technician with a scanner could access codes and data for you. Typically, erratic idle could be caused by carboned-up throttle body, an airflow sensor (MAF) that's out of calibration due to a defect or dirt. It could be caused by a sticking exhaust gas recirculation (EGR) valve. If you want to find a Mazda specialist, here's a directory link for You: https://repairpal.com/mazda-repair-in-new-berlin-wisconsin