Low Engine RPM on Warm Engine Start (1994 4Runner Auto)

I have a 1994 4Runner 4WD Auto with 176k on it. I hope some experts
here can shed some lights.

Problem:
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- If I start a warm engine, the engine rpm fluctuates between 100 and
400, then eventually it falls back to zero and stalls unless I start
shifting to drive immediately and start driving, then everything will
be normal.

- If I start a cold engine, everything is normal.
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Question:
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Why does it only happen when the engine is warm? Could this be
related to the fuel system? But again what part of fuel system will
have troubles with a warm engine?
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Any help will be appreciated!

- Superjunkyard