[Blue Bowtie]

Warmup without load until the coolant temperature is at least 100ºF is always prudent, despite what the self-proclaimed geniuses at the U.S.E.P.A. might say they know about fuel mileage and pollution.

Engines waste a lot more fuel, emit a lot more pollutants, and wear a lot faster when run under load at cold temperatures. That wear will cause a lifetime of pollution and waste, compared to a minute or 90 seconds of running unloaded while warming up every morning until the coolant (and head) temperatures are sufficient.

If the ignition system in intact, what you are experiencing may be due to the necessarily rich mixture needed to get the engine started and keep it running until it is sufficiently warm to keep the fuel vaporized as it is injected. It the car is driven in this manner, even under light loads, the rich mixture can cause poor combustion, misfire, and contamination of the spark plugs, chambers, and engine oil. This will shorten engine life and cause you to waste more fuel and pollute more over the life of the vehicle.