I'm not an engine guru but here goes my question:

How does the engine computer decide which injector to use between port and direct?

I want to avoid carbon build up and we all know port injection solves that problem. But how do I know when the engine uses those injectors? Is the switch over rpm based? Throttle positioning? Speed dependent?
I do Italian tuneups on my cars once a week and I want to be sure that I do it right with my ES 350.

It varies depending upon engine temp, rpm, and load. It uses one, the other, or both depending upon which combo gives the optimal burn for the given situation. It’s brilliant and amazingly effective.

This video will explain it. Not for your car exactly but it’s the same in application. Nothing you need to do driving differently because of it. The main benefit of a Guido tune-up in these is keeping the lower tension rings free; the FI pattern won’t matter much wrt the “tune-up.”

https://www.youtube.com/watch?time_c...M5MTE3LDI4NjY2

Attached is a 2006 SAE Technical Document on how the D4-S operates on the 2GR-FSE when it made its debut on the Lexus IS350.

Thanks!
So the wider the throttle, the more direct injection only the engine becomes.
Around town driving it's a combination of both.
Genius!

It's a very good system, high power is mostly DI for precision and control to take advantage of the higher CR without risk of detonating. Steady state can and is port because it's far easier to have the desired mix ratios under cruise conditions, plus it cleans during this time.

Big credit to Toyota for debuting their DI system early and in a very good state unlike the others.

and they were saying the ICE is dead ! pretty cool to learn about d4s!

so tech went from carburetor, to EFI port, to direct, to both port/direct - what's next?!

To be fair this is over 20 year old tech.....

The computer uses both. Port injectors run more at low speed and cold starts. Direct injectors run at high speed and heavy load.

Your Italian tune-up is the right method. Sustained high-RPM driving is what forces the port injectors to work and clean the valves.

For best results, use a top-tier gasoline like Shell or Chevron. Their detergents help with cleaning.

High load/RPM is all DI...

Correct, that was my understanding as well, in order to provide the best power delivery, DI is used exclusively at higher throttle applications. Port injection is used at low load situations and sometimes at idle (specifically, it cycles to port injection sometimes to clean when idling for extended periods). Either way, an Italian tune-up is still fun and probably won't hurt anything if the engine is healthy!

In my IS 500 I can hear it making this switch from port to direct if I am, for example, in a drive-thru lane for a while. I try not to idle it for a long time, but it does happen... and I've also noticed it doing this while shooting photos before. The ticking sound from the engine briefly goes away when switching to port injection at idle.

Indeed it does, took me a minute to get used to that in my LS. At first it was disconcerting because the tone of the engine changed

It took me MUCH longer to get used to the DI at idle; it sounds SO wrong when you know it’s a gas engine and not diesel! But you are correct, if you are a “listener” it’s always disconcerting when a tone changes abruptly on most any machinery.

And I 2nd what you said above about how impressive it is for a) first attempt at the tech, and b) 20 years old already, and most manufacturers can’t get it 1/2 as good. I view it as a tremendous statement about Toyota’s engineering prowess.