Why does my neon stop running above 70 degrees

Matt, without having all the information, here are a few common causes. Most likely is secondary ignition trouble. The next most common issue is a sticky EGR valve. The valve is supposed to open while driving to reduce engine emissions, if it doesn't close properly it will cause it to run rough, buck, and stall especially when you have to come to a stop. The other possibilities are idle control valve, throttle position sensor, camshaft position sensor, crank position sensor and vacuum leaks. They are the easier ones to check. With your engines warmed up and running, using some WD40 and gently spray around the vacuum lines. If the idle straightens out, you have found a leak. Replace the line (or fix it) accordingly. Of course, make sure that you change your plugs, wires and properly service your engine as well. When you change the plugs, take a good look at the face and see what color it is and what the overall appearance is. It will tell you a lot about the way your vehicle burns its fuel. Hope this helps to get you started. Good Luck.