The ecu looks at the exhaust O2 sensors and adjusts the fuel for a proper air to fuel ratio.
That's only in closed loop, which isn't happening on startup.
Wide open air intake, engine cylinders position saying the crank is turning, and at the proper time it will fire the sparkplugs, O2 sensors say lean,
The oxygen sensor input will be ignored, because it won't go into closed loop with no TPS signal.
air fuel computer map combined with engine temperature sensor(s) and or coolant temp sensor(s) and it will supply fuel when it should unless there is some code written in the computer for sensing something is so wrong that it should not run.
So, it depends on what the programing of the ecu looks at and what it is seeing. And that can vary with different makes and maybe even different engines and or models of even any brand.
This hinges on whether the ECM will still fire the injectors with no throttle position sensor. If it will, a couple things are possible:
1. If the vehicle is MAF, it will see 0 airflow and either:
- assume the MAF is bad and go into base table, so just idle levels of fuelling and immediately lean-stall
- or, assume MAF is correct and there is no airflow and lean stall.
2. If the vehicle is MAP, it will see no vacuum and either:
- assume both it and the TPS are invalid and go to base table fuelling, lean stalling
- ignore the lack of TPS and go to 100% load fuelling, going off the rev limiter and possibly blowing up.
Computers can't think (at least not yet). They execute programs that are prewritten using data put into them from sensors. And some companies spend more on programing than others, so there can be different results when unusual input is put into the ecu depending on the programing.
Yup, some use redundant POT's to confirm sanity of inputs, some don't. I had a TPS go bad on my Mustang, which increased fuelling and it started idling at like 2,500RPM, lol.