ITB convert need standalone ECU

[Bean]

This is a very loaded question. I'll try to keep the answer short.

The stock ECU has only very marginal capabilities to adjust for changes. Fitting ITBs changes the MAP signal drastically. Therefore keeping everything else stock you will not just loose some power through the range but it will also affect driveability an fuel consumption.
Now add a set of cams and the ECU is definitely overwhelmed.
This is all considering a MAP controlled engine. If the stock engine was running an AFM the ECU can't control a MAP signal at all.

Long story short going for ITBs for performance reasons is in most cases only necessary above 160hp @ engine and that's aiming very low. More realistic is 180+ and even in those cases a bigger or altered throttle body would do the trick just fine. Most people change to ITBs for the looks and sound alone.