Mark, Once again, besides DK's, I'd check sensors. Your symptions sound similar to my problems with the cam position sensors (pulse sensors). First time it happened - cold start, one bank only. Warm up the car, restart it and everything was fine. Replaced one sensor and cleared it up. 4 months later, car goes into Transmission Fail Safe mode and after a lot of troubleshooting, it turned out to be the sensor on the other bank. We got multiple error codes so things were confused for a while. The electronics are so integrated, that a failure in one sensor can trigger fail safes in other systems (e.g. engine sensor triggering trans fail safe). The sensor was $125.