I have a tbi 94 geo tracker that started with the same problem as yours but now it got so bad it will only idle below 800rpm. I am a Maintenance mechanic Manager for a plastics manufacturer. I was not impressed with the dealers I can't check it bull so this is what I did.
got the chilton manual.
The oxygen sensor is not suppose to be able to kill the engine the book says. The computer operates on a 5 volt dc system.
checked the map sensor 5 volts in from computer. proper volts through sensor and I even fed 0 to 5 volts back with a power supply.
checked the throttle position sensor. 5 volts in from computer 0 to 5 volts back to computer through range of pushing throttle lever.
I then put a volt meter on the throttle body injector to check for 0 to 5 volts from the computer to open a little or a lot of gas into the intake.
THIS WAS THE PROBLEM! THE COMPUTER WAS NOT OPENING THE INJECTOR WITH 1.2 VOLTS AT IDLE OR 4.5 VOLTS AT FULL THROTTLE!
IT WAS ONLY PUTTING OUT .8 VOLTS AND BARELY KEEPING IT IDLEING AT 500 RPM.
I found many references on the internet of the computers going bad on these models early!
All the dam dealer has to do is hook up a cheep voltmeter to the throttle body injector or each of the multi port ones and check for 0 to 5 volts as you push on the gas pedtal. I don't think your money should have been spent to train thier factory trained mechanics so ask for it back or go to small claims court the judge will agree don't build something you can't troubleshoot.
The circuit board guys say leaky capacitor acid corrodes the board and makes the ecm computer erratic and fail.only some can be repaired. time and heat are the enemy.This makes me wary of used parts.Low milage vehicle ok? 1700 DOLLARS CANDIAN FOR NEW ECM. Anyway I will buy a whole spare car or wire in a compatable unit from something else. Used computers range rom 200 us. Leave yours hanging and go buy it and put it in to try it first.You might get a electronic repair before its to late. Good luck.