In an interview with Top Gear, Tobias Moers, CEO of AMG, says that finding a stable idle was the toughest part.
"Getting a stable idle at 1,200 rpm, that's challenging. To give you a simple example. You have leakage in the throttles in Formula One, and nobody cares, because it runs at a 5,000 rpm idle. At a 1,200 rpm idle, you have to meet the emissions regulations. You need a stable, proper idle. If it's unstable, your emissions are unstable."
When the objective is to make maximum power, emissions don't matter all that much. Still, a 1,200 rpm idle is really high for a road car. It's clearly worth it to AMG and its customers to make it work with this engine, though. Here's what Moers said about feedback from the people who are waiting for their cars: "You know what they tell me? 'Make sure that the car works. Because of what we experienced in the past with hybrid cars, take your time.'"
So, Mercedes still intends on delivering an incredible hypercar with a modified Formula One engine, but it doesn't appear to be going silky smooth. We don't think anybody's surprised about that, though; Formula 1 engines were never intended for a road car application.