I also believe that letting a car idle to "warm up" does nothing good and wastes fuel. Start it up and drive away. But don't romp on it until the engine oil is at normal operating temperature. I know, you don't have an oil temp gauge. My unscientific, unsupported-with-evidence rule of thumb (ROT) is that it takes the engine oil 3 times as long as the engine coolant to warm up to normal operating temperature.