there's a common problem with knock sensors on this car

id be very hesistant to accept a diagnoses of the ECM without substancial proof and thorough explanation as blaming the ECM is a tactic often taken by inexperience mechanics

naturally, it would have been wise to get our opinion on this before having them replace it, but suit yourself

 

I do not see any mention of what the code is? What tests were ran before the "mechanic" condemned the ECM?

And by far most important, what if any tests did he do the verify that the crank sensor is good? A intermittent crank sensor will kill the engine and act like the key was turned off. But it will not leave any codes. For the symptoms that you describe I would STRONGLY recommend checking the crank sensor before replacing the ecm. Cranks sensors have a significant failure rate, ( higher than ECM's).

 

I second this: