I have a P0521 that goes and comes. Started about 2 months ago, swapped It out with a Advance auto one code went away for 3 weeks then came back. Swapped It again and the code came back the next day and started to puke oil between the sensor and electrical connector. So I had no choice but to put the original sensor back on. Installed a new a OEM AC Delco sensor and also replaced the screen under the sensor (dorman) and the code disappeared for a few days and came back. Now the code has been gone for about 2 and a half weeks and this morning we got a little snow storm and the car has been off for about 17 hours In the cold snow. I remote started It and listened to It start up cranked weak but started and the engine sounded fine no lifter noise. It ran 10 minutes and shut Itself off. I started It up again and within 10 seconds I heard It shut off. Went out and manually started It and the engine light Is on with P0521. I'm at a lost here. I always let It warm up before taking off.