I'm sure we could all benefit from a complete fuel & vacuum hose replacement. None of our cars are even near new, right? BMW used a rather poor, in my opinion, grade of fuel hose, and I replaced miles of it in the late 80's-early 90's. It would look fine, but it would "sweat" gasoline. Customers complained of a fuel smell after turning off the engine. Some 750's burned because of this. Vacuum hose wasn't any better. I used to replace all these with Mercedes hose, the stuff with the cloth braiding on the outside, then M-B started using exactly the same junk hose as did BMW.
In the same light, the ECU is a very dependable part. The problem usually does not lie there. Temp senders can go bad over time, and there's a good place to start. Check it cold & hot, as it can fail on either end of the range. Still, my $$$$ are on injector leakdown, or leaky fuel hoses, and the latter will be obvious by the smell and the gas stains in the area of the fuel rails. The air flow meter has a potentiometer under the black cover that can wear out, and cause driveability problems of all sorts. This usually worsens over time.
Lucky me, my iS runs like a champ. starts fine, hot & cold. I'm counting my lucky stars......
