High idle when hot outside
 

Why would our 01 Maxima rev high when its really hot outside and it has been driven in stop and go traffic or sitting in traffic?

What do you mean by really high? What's the rpm at idle. I'm assuming it is more than 1k which could simply be from the a/c. Gotta give us some details.

Yes, some engine rpm numbers would be helpful.

But the a/c should not cause the idle to increase. I don't know if the engine overheating would cause that, but it might. What does the temperature gauge indicate?

Maybe you need to check and see if both of your radiator fans are running.

It normally idles around 800 or so in Drive with the AC on. When it starts to act different I can feel it and if I put in Neutral or Park the tach goes up to around 1500. I can turn the AC off and it goes a little higher. The temp gauge is always normal, at not quite halfway. It has never overheated, even in almost 100 deg weather last month.

I wonder if your throttle position sensor is in need of adjustment or replacement.

To a much lesser extent, I wonder about your IACV (Idle Air Control Valve) being messed up. But this should give you a check engine light with code P0505.

I do have a check engine light on but Im not sure what the codes are. I am not a mechanic or anything but I do try to keep an eye on things that do not seem right.

Take the car to an auto parts store and ask them to check the codes. It is a free service offered by all the store chains. Unless you live in California...