Have you recently changed to a thinner oil (or has it been a long time since the last change)? Also, hot weather can thin out your oil tripping your pressure sensor.
It could be an oil pressure sensor on the fritz. This is a fairly common problem with these cars- it happened to mine. On my car, it was the oil pressure sensor on the side of the motor. It looks a little bit like a spark plug with a rubber boot and a wire sticking out if it. It may even be leaking a little. That's a good sign it's bad. There's usually another one on top of the oil filter. Try looking up the part on autopartswarehouse.com (or wherever) and seeing what yours looks like. They're fairly inexpensive and pretty easy to replace.
Good luck!