Not all the time, but maybe one in 25 I get a start fail.
My 2003 4.6 does this:
Sometimes the engine will start and then immediately die.
I have found that if the AC is on it doesn't die.

Also, I have turned the key, and nothing.
No crank, no click, no nothing.

ALWAYS, starts on the second try.
Battery is Interstate and 6 months old.

Car has 62 K miles and idles rock steady, no check engine lights,
Runs like a scalded Impala.

Wanting to track down this intermittent problem.

Any thoughts?

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2003 4.6is X5
2003 525it
2003 E53 X5 Standard shift