A C421 PLT; DURING CRUISE AT FL240; EXPERIENCED AN ENG PROB; RESULTING IN A DEV TO NEAREST SUITABLE ARPT.

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WE WERE FLYING AT FL240 WHEN I NOTICED THAT THE L ENG OIL TEMP WAS AT RED LINE AND THE OIL PRESSURE HAD DROPPED FROM 50 PSI TO 25 PSI. I NOTIFIED ATC AND REQUESTED AN IMMEDIATE LNDG AT TWIN FALLS; ID. AFTER BEING CLRED TO TWIN FALLS; I BEGAN A DSCNT IN VMC CONDITIONS ABOVE A BROKEN LAYER. DURING THE DSCNT I WAS REVIEWING THE SIT AND CHKLISTS AND MAY HAVE EXCEEDED MY DSCNT CLRNC. THE CTLR WAS EXTREMELY HELPFUL AND NEVER MENTIONED AN ALTDEV; BUT WITH ALL THAT GOING ON IN THE COCKPIT; I DO NOT RECALL EACH OF THE DSCNT CLRNCS. I SHOULD HAVE DONE ONE OF A COUPLE OF THINGS: I SHOULD EITHER HAVE DECLARED AN EMER OR TAKEN A DEEP BREATH AND HANDLED THE DSCNT JUST AS ANY OTHER DSCNT. I PURPOSELY DID NOT USE THE AUTOPLT BECAUSE IF THE L ENG FAILED I DID NOT WANT THE ACFT ON AUTOPLT. HOWEVER; I HAD PLENTY OF TIME AND ALT TO DO A SINGLE ENG APCH IF NECESSARY. I WAS TOO ANXIOUS TO GET THE AIRPLANE ON THE GND. EVENTS BECAME BLURRED IN THE STRESS OF THE MOMENT; BUT THERE WAS NO REASON FOR THAT LEVEL OF STRESS. I WAS WELL TRAINED; CURRENT; AND HAD PLENTY OF ALT AND AN ARPT WITHIN EASILY REACHABLE DISTANCE. THE BOTTOM LINE IS THAT THE ENG DID NOT FAIL AND THE PROB WAS TRACED TO A FAILED VERNATHERM.