I have an older, low mileage vehicle with a V8 engine. When the engine is started cold, regardless of the outside temperature, the idle is rough and there is a noticable power loss. However, once the engine reaches FULL operating temperature the idle is smooth and power returns.
During the rough idle, I notice the tach needle quivering and that the engine is revving lower than normal. Also, there is an economy meter, fed off engine vacuum, which reads “lower than average” economy and its needle also shakes.
Some folks have told me to check the ignition system, others the vacuum system. Any thoughts would be very welcome!