Common sense says to check the transmission fluid level and quality. There’s several possibilities, need some preliminary work to bring the routine maintenance up to spec and some more diagnostic work done before making some guesses what parts need to be fixed. This is what I’d do with that problem if it occurred on my early 90’s Corolla 4 banger.
If it hasn’t been done recently, replace the spark plugs and engine air filter.
Idle rpm and ignition timing check
Ask you shop to check for a plugged cat or exhaust system obstruction
Measure the intake manifold vacuum
O’scope ignition system test
Compression test
Fuel pressure test
Fuel trims test
They might go down as the transmission shifts up to a higher gear, that’s normal. If this seems abnormal to how the car worked before all this started, when you step on the gas the EGR system gets actuated, and the intake air flow, exhaust air flow, and fuel flow are all stressed to the max. So it could be any of those. A fuel pressure test during driving would be where to start if nothing else was obviously wrong.
Thanks for the feedback, looks like we all got skunked. Nobody mentioned anything about coolant temperature … lol … I think a shop would probably do a basic scan tool check as one of the first tests w/a problem like this, and one part of that would be to see what the engine coolant temperature sensor is saying. That would have sussed the coolant temp sensor out as the culprit in short order. A fuel trim measure would have led a shop to the same conclusion at some point.
The computer uses a coolant temperature as one of the most important parameters in its air/fuel mixture equations. When that parameter isn’t accurate it confuses the computer and it can’t figure out how much gasoline to inject, which could create all sorts of weird drivability symptoms. You’d think the computer software would be smart enough to know that when the engine has been running for 15 minutes the coolant temperature should be around 190 deg F, and if it wasn’t would throw a coolant temp sensor code, but apparently not in this case. The p0773 is presumably a red herring.