Throttle problem on warm re-start in hot weather.
 

Today the temp was over 90° and I was out for some freeway and spirited driving. I stopped somewhere, and about an hour or so later got back in and started it up. She started up just fine and idle was rock solid, but when I pressed the throttle, the engine speed just oscillated between 1000 and 2500 RPM no matter how open the throttle was other than closed, then it returned to rock steady idle. This condition lasted for five minutes, and then she just ran fine.

A little background. The engine is totally stock NA. I just replaced every gasket, O-ring and seal on the intake. New plugs and wires. All the vacuum hoses have been replaced with silicon, and it passes California smog with flying colors. Any ideas what the problem might be?

Oh, another thing is that my voltage occasionally drops down to 13v for unknown reasons. Maybe there's an electrical problem. I've also noticed that some of the wires in the engine harness are brittle and cracked.