87 na 13b s4 no real upgrades, i have checked everything and all the electrical componets and fuel components every seems to be good. the car runs great for the first few minutes then the trouble begins. it starts bucking and back fireing. all the time its at different rpms and dosn't act like the 3k hesitation problem. check with a wideband and when its running good getting 14.10 reading but when it goes bad its real lean. Sounds like the fuel fillter or fuel pump right? well check both of those no problem with ethier correct fule pressure and fillter is brand new. so i changed the injectors thinking that may be it, nothing still the same. changed the trailing coils still no luck .......but when i did that i lost my gaudges no tach, fuel, volt ect. went thru and cleaned up all my grounds that i did before. i am lost ...any ideas would be great

 

check disty

 

did check it no problems

 

Check the o2 sensor. Many people misdiagnosis another problem for an o2 sensor but this sounds like it could be your problem. Could also be your ECT. Check both. The car will run closed loop on start up and then until warmed up, then will switched to open loop using the o2 sensor readings. Sounds like your car runs fine in closed loop but not in open loop. Hope that helped or atleast puts you in the right direction .