Play the mission where you must chase down Warren and destroy his car. If you lose sight of Warren and his car, immediately get out of the Mag (King's car) and get back in. The timer to catch up to Warren will be gone and all you have to do is track him down. You can use this as many times as you want. Immediately fix your car. If your car is in bad condition, go to an activity marker. Make sure that you cover up half of the marker with your car, then get out and start the activity. After the scene, your car will disappear. Wait a couple seconds and a new car should drop down where your first car was.