So for the last week or so, my '90 535i has been having difficulty starting. More than half the time, when I turn the key, the engine will crank, but it doesn't sound like it's even trying to start (no sputtering/etc). If I stop turning it over and try again, it start almost immediately. If it does that the first time, it ALWAYS starts on the second try, almost immediately.

The problem started abouta week ago, after a weekend road trip I was taking. I can't remember if it started on the way back, or after getting home. The only thing that's been changed in the car in that time is the gas.

Any ideas where to start looking?