Actually, the "Throttle Body" injectors used on GM 350 ("K" engine code) 8the digit in VIN #.... are peak hold injectors. They use 2 very heavy duty "driver" transistors in the ECM, and they get tired after so many years of use, and hash (not the kind you smoke!LOL) can be seen on the voltage line with an Oscilloscope. What to do? Go thee to Radio Shack and purchase 2 0.1 microfarad capacitors and solder each one across the injector right at the connector under the air cleaner. I did this on my 1990 Suburban 4 years ago. She has idled much smoother since, gets 2 MPG better mileage, and passes emissions with flying colors! And with almost 185,000 on the odometer! All original,too!
As far as the oxy sensor goes, new ones are cheap... and fairly easy to replace. ALL Electronically Controlled engines go out of closed loop at WOT... This is the clear flood function whereby the fuel pump is disabled during crank. It is also how I can perform a clear diagnosis on driveability using a scope. Snap throttle to wide open takes the computer out of the loop and enables me to find bad injectors, etc. You can also scope the oxygen sensor and "see" bad injectors..