Well, I finally got around to pulling the trigger on replacing the O2 sensor on my '93 VX. Tried the less expensive solutions like replacing the TPS, cleaning the EGR, cleaning the IACV, New Plugs, New Plug Wires. The $160 NGT O2 sensor found several places on-line did the trick. I'm sure the one on my car was the original, as it took my 1/2" air ratchet to break it loose and I busted a nut removing the heat shield, but I'm fine driving with just one nut and a smooth throttle. The surging was so bad it was difficult to tell if the Progress CS-II suspension was to blame, but now I know it was the lean-burn transition and not the suspension. Just wanted to post since I've seen lots of similar throttle response issues posted over the years.

 

Great to know you fixed your issue.

I actually bought that O2 sensor and had a "chugging" at idle from the O2 response since that sensor uses a different voltage drop than the factory sensor. It was annoying only for the fact that the idle would serge but only about 50 RPMs. It would drop and raise about 50 RPMs which you cant even see on the factory tach but could feel a vibration difference and made acceleration from a dead stop a little jerky out of lean burn mode. It transitions in and out of lean burn well but was never perfectly smooth when not in lean burn during acceleration or deceleration.

I ended up taking it out and buying an OEM o2 sensor to test the difference and it is night and day. the OEM sensor looks identical but has a different part number stamped on the sensor itself and makes the car drive so smooth you would think its a brand new car even though the odometer says over 260K. without my MPGuino i cant tell if im in lean burn mode or not because it transitions so smooth and seems to have better response while in lean burn. I can actually stay in lean much longer now

but with all that said, i paid a premium for the OEM sensor. I think out the door was $380 for the sensor.