That sounds like a pretty good guess, usually when the 02 is going bad your fuel economy goes bad too, have you noticed that?

 

on obd1 youre knock wont pick up small things ie miss fire,bad o2. thats why all new cars have a millon senscore where the older cars dont. you may not see a drop in fuel ecom, the o2 has a hot/warm and a cold setting, so it sounds like thats where youre having issues. when i got to work ill get you the read out for a bad o2 and you can see if it mattchs.

 

Yea, my fuel consumption is about 17 / 17.5 on highway, thats about as good as they will do I believe.

 

use an obd2, and x2 on the o2 sensor, or the temp sensor

 

WHAT?????? what are you talking about Iceman?

 

My first thought is O2.
Prior to warm up the truck is in open loop (not using the O2's). Once warm...it goes into closed loop and the O2's adjust fuelling.
I'd replace the front O2's. (if that model has rear O2's..so 4 all up...they only run emissions checks and throw codes accordingly...have nothing to do with fuelling).

 

I have the same problem with my 95 gmc,it was running rough I replaced the s-plugs and it ran great for 5000 miles.1 week ago I was driving with the cruise on and the engine started to surge and lose power it down shifted just to hold speed.No dash light on or codes.The engine starts and idles fine in park,runs rough in drive and and on accleration it has not much power(sounds like it wants to go but it wont)it surges and gains power in rpms over 2500.I have replaced fuel filter,o2 sensor,dist.cap and rotor,plug wires,egr is ok.Iam fusrated since I have owned GM trucks all my life and never so many problems.Truck has 206,00 miles with new GM long block at 158,000,(crank shaft broke in half).

 

I have seen this proublem several times, try checking the distributor sometimes the advance ring is loose and makes the timming wrong. Good luck

 

I HAD the same problem.... ran fine till she warmed up or sometimes after a restart and then the surging and missing would begin. no codes. 7000 dollar snap-on scanner told me nothing. I had a rebuilt motor. changed the distributor, ecm, the mass air flow sensor, fuel pump, tps, plugs wires, temp sensor and wire, cats and muffler were already new and for my efforts I was rewarded with hiccups and dead cylinders. NOW MY SOLUTION WAS : THE OLD STYLE POPPIT SPIDER INJECTORS WERE GARBAGE.... I installed the newer multiport injection unit and she runs like a dream. my 220000 mile sub runs like a new car again.... hope this helps someone else.

 

Im having the same trouble and im thinking this is the problem. Same as you ive changed everything else including throttle body and injectors, plugs, wire, cap, rotor, coil, MAP sensor, etc. The ETCS will cause the symptoms. not sure if this helps but hope it does as well as mine! The way i understand it is that this sensor is not a coolant sensor but im just not sure. maybe someone else will know what im talking about.