Sorry I have not replied to you sooner, did not mean to leave you hanging but I had family health issues that take priority.
Last time we talked you suggested checking the o2 sensor.
1) Original o2 sensor heater element showed no resistance; and real-time o2 output
measured at ECM was .020-.080v instead of .200-.900v, crossover was approx
1x /sec @750, 2x /sec @2000 rpm. Amplitude low but frequency good.
2) Checked circuit integrity of o2 heater and signal: good
3) Replaced o2 sensor with oem Denso.
4) New o2 sensor heater element measured 3.5-15ohms; and real-time o2 output
measured at ECM was initially .340V for 30 seconds then dropped to .020-.030V at
750rpm; .060V @2000rpm @45mph cruising at level, and .200-.720V @ 2000rpm cruising uphill.
5) Performed back pressure test utilizing the o2 sensor hole. There is only one o2 sensor
and it is located pre-catalytic converter.
Result was: 0.5psi @750rpm, 1.0psi @2500rpm, and 1.5psi with sudden throttle.
6) Final result: car performs with same symptoms of hesitation at partial throttle at any speed but not as bad. Car hesitates and stumbles then seems to clear up then strong acceleration.