Rough idle when cold

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This Ranger has only 80K miles and has been babied since new. Recently it developed a rough idle when cold. Runs great once it warms up. Recent code indicated an 02 sensor which was replaced along with the check valve grommet for the power brake unit. Replaced the idle throttle position motor to solve an idle surge problem. I can't find a vacuum leak. I haven't yet checked the intake gasket or "0" rings. I have heard a fuel injector "0" ring leak can cause a rough idle. Recent tune up with plugs, wires. Coil checks OK. Any more ideas?