My 1990 1/2 ton Club Wagon has a 351 FI, E4OD and a 3.55LS.
More than half the time, but not all the time, at low RPM and light throttle, I have a bad "miss." Honestly, it's more like bucking than missing. It happens especially badly at around 45 with the tranny in 4th, TC locked and just enough throttle to keep it rolling at the same speed. Incidentally, it's not as bad when it's cold.
My estimation was that this was ignition related since that's the times where I'm likely to have the most strain on the firing of the plugs. However, I've replaced the plugs, wires, cap, and rotor and seen no real change.
I pulled the codes and the only hard fault I have is a 44, which deals with the air pump system. I haven't found out what the cause of that is, but I wouldn't think that it would cause this. The van just passed the Northern Virginia emissions inspection with flying colors, so I'm surprised that there's a fault in a part of the emissions system.
I also had an old EGR related code that I only got from the KOEO test. I'm more likely to think an EGR problem would cause the bucking I get.
Lastly, I tried to do a cylinder balance test, but couldn't get the thing to go into the test after the KOER portion. I tried tapping the throttle, as my scanner book suggested. I even tried a brief WOT.
Any help?