i did the same. i followed all wires from the ecu to the sensors, cross checked continuity between the vta1 and vta2 as well as the afm. the blue/red wire has full continuity, with no resistance at all 4 points, and crossed between the sensors themselves.
i even snagged a tps plug from a junkyard to use for testing purposes. self grounded the tps out of the harness, with no help in the matter. bridge patched the connector in with an old tps, and the plug that way i could check all voltage and signals while the cars, running. all was fine.
so i did the same with the afm, same story all is well back to the ecu as well.
im getting 4.99 volts on idle, and 5v as soon as i crack the throttle, so its definitly not a voltage problem. the variable resistance potentiometer (tps) can develop a "flat spot" in the sweeper, but not likely 3 different units have the same issue, besides ive watched all 3 on a multi meter while actuating the throttle.
all the sensors are fine.
the more i read, the more im finding the ecu is a culprit. mind you im also finding in my personal searches, the 93-94 ecu, especially a good working one, is like trying to find a diamond in a gravel pit. my first ecu (50141) gave up on me about 1.5 months ago to the point the car wouldnt idle above 300 rpms sometimes, and after a warm up the car wouldnt idle down from 2000 rpms. trying to blip the throttle or increase throttle was impossible. the car would spit, backfire, and pop.
during this spill of confusion i replaced both cam angle sensors, checked all the wiring for the CAS, replaced the crank angle sensor, checked its wiring. replaced the tps, checked its wiring, and replaced the afm, all while checking everybit of wiring, so i know its not my harness nor the sensors, and like mentioned before, since tps's are pocket items ay junkyards, ive tried 3 different ones. same with afms. i tried 3 different afms, all in spec, with no issues.
so i yanked the ecu to have a look. found 5 different capacitors that were suspect. so i replaced them, with no added benefit the car ran the same. so out of desperate measures i purchased a junkyard ecu (50142) out of a 94 ls400. all the previous symtoms went away, but this sympton appeared. the very symptom thats plaguing me and you both.
so i did the same, i opened this junkyard ecu, to find there was 5 popped capacitors as well, some the same as the other, and some different, meaning on different circuits. i replaced them as i did the original ecu. but it still did not fix the issue.
however i found a local guy to me here in my city that offers an ecu "rebuild" service and says he can take any dead ecu and make it work. so ive been communicating with him via email, and he accepts the challenge of repairing the 1st ecu (50141) or i pay nothing. i made him aware that i had already replaced the capacitors and looked over the board with a flashlight looking for swollen resistors and other isues, and the problem simply seem to lie in an issue with the fuel managment part of the ecu data being corrupted. he thinks he can fix it, so if all goes well, ill also get my current ecu looked at as well. ill report my findings back here.
honestly this issue is becoming a bit of an annoyance. the 93 ls400 is a big car and somewhat heavy. getting into traffic is a bit of a pain under 60% throttle. also living in a mountainous region, even interstate driving on some of the hills i fall down as far as 45 mph from 70mph, simply because i cant push the accelerator far enough to downshift. i long for the day i can once again floor my ls400 and hear the 1uz scream.
... kidding but seriously stumped... thought about the factors that control the fuel cut and there is really only 1 component that i havent checked and that is ecu... maybe i can bridge something on that side i just dont know!!! help help help...
