A colleague recently arrived at the office in my BMW 320d about 90 minutes before I did, and when I parked next to it I noticed the engine was running.
It turned out he’d parked, and the stop/start had closed down the engine. He’d then got out without properly shutting the car down, locked it and walked off without another thought. After a few minutes, the stop/start must have kicked the engine back into life, where it sat on idle for the next hour and a half.
It was clearly user error, but the keyless start didn’t help in this situation as you don’t have to remove a key to turn off the car. Ditto the fact that the radio stays on, even when you do turn off the engine, until you get out and lock the car.
While we’re taking the blame for the mistake, it’s surprising that it’s so easy to make a quite basic error that could have had serious implications if it was locked in a garage, or had been left all day and run the fuel tank dry. As it is, it’ll be interesting to see what impact it had on this tank’s fuel economy, and it’s probably negated the stop/start’s benefit over the 10,000 miles so far.