Have a 2004 F150 when fist start up in the morning after the rpm comes down I get a rought Idle but as the engine gets warrm the idle is smooth. if I hold the rpms back up to 1000 when cold the rpm's go up and down a little but runs fine when warm. Had it in shop and could find nothing wrong except on #3 showed a miss when cold, replaced coil pack and plug but still the same. Help !!!!