Year 2000 SL320. Engine turns over after turning key and continues to turn over for 10 secs or so - engine does not fire. Tried this for 20 mins or so, in P and N. Locked the car, opened the car, shut the soft top, foot on brake and everything else I could think of. Got a lift to my appointment came back 2 hours later, tried again and it started first time. Something to do with car immobilisation system?