86 325 es intermittent no-start

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Hi all,
my wife has an '86 325es that has a highly intermittent no-start condition. It may start fine for a few weeks, then will crank but not fire at all. Eventually, it fires right up, and once it's running it's fine. I had replaced the crank pos. sensor to no avail. Beginning to think ECU, but wanted to ping people here to see if there was a consensus as to cause.

Thank you in advance for your time!!