What may cause for RPM to suddenly fall when start?

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Starting my 2008 ML350 in cold weather (in the morning when vehicle stays overnight) results in sudden RPM fall to below 700 with 2 sec ticking sound under the hood. Check Engine light comes blinking and then stable with error code P030X (sometimes random P0300 sometimes from P0301 to P0306). If engine is restarted then Check light disappear. Only happens when it is below 70F outside.