I recently bought a 2003 Civic EX automatic 3 weeks back. Last week I changed the oil. Since then (not sure if its related), every morning I face a problem. The car starts fine and seems fine while on parking. But when I put it in drive and drive about 100 yards (gears shift meanwhile) and then come to a complete stop, the car does not pick up after that. I starts vibrating like its stuck in higher gear, the RPM drops to about 500 rpm. I either have to shift to neutral or switch it off. Then on, there is no problem for the rest of the day. NExt morning same problem occurs.

Also, Yesterday, I warmed the car up for good 3-4 minutes, then this problem did not occur at all.
Any idea whats wrong with it?

Thanks.