i find this warmup proceedure succesful on short trips in sub zero temp. start motor,allow to run at normal high idle,idle will decrease slightly after variable times depending on weather,idle will further decrease after variable time to near normal idle, apply gentle throttle to 2000 rpm, allow to idle for few seconds, rev to 2000rpm,allow idle a few seconds,rev to near 3000rpm,allow idle few seconds, repeat this few more times then rev to 3500rpm,allow idle then drive off gently. after 200 yards try to apply power load so that car is using lots of fuel but do not rev over 3000rpm and only do so if road has grip, no need to go fast , slow again if possible then accelerate again gently, i use this proceedure regularly,if engine is working to accelerate car then much fuel is being used to warm engine. i always run engine 15-20 minutes to warm up and recharge battery power used by starter.