I'm about to give up and go to the dealer. 97 LS400 - 148,000 miles really nice shape. My saga started with rough running. Took to local highly recommended independent. He "checked" ignition, compression and whatnot and said we must have gotten some bad gas. Drained and added a litttle. Said there was some "white stuff" in the gas but couldn't tell what it was. Also told me he would have changed the fuel filter but that "model didn't have one". He said it seemed better and I thought I'd better get her outa there before he tried to fix something else.
I had ordered a engine temperatute coolant sensor -that shows up a lot in the troubleshooting section of the factory manual - which I have - and I was blaming for very extended shift delay when cold so I changed that -seemed to help the shift, by the way. And I changed the fuel filter - in back above and to the left of the differential and dumped in a can of seafoam.
Ran OK for one or two short trips - then rough again. codes were 0300, 0302 and 0308. Random misfire, and misfire cyl 2 and 8. I started changing ignition parts - plugs and wires. NG - rotors and caps - NG. always would run OK for a minute or two - just long enough to get out of the yard but would shortly start missing again.
It would rev up OK, slowly, and always threw 302 and 308, so I figured the fuel system was OK and started working on the injectors. All new to me but with my trusty manual to guide me, I tested all of the injectors. Ohmed them - all met spec. Built a test rig to test fuel flow quantity - all tested OK -(kinda scary fooling with gas and sparking wires!). Put it all back together but moved injectors 2 & 8 to positions 4 & 6.
Different, but worse. Now missing on 3,4,5,and 6. But 2 & 8 OK so ordered two injectors and all of the o-rings and gaskets to put it together right. Got it all together this last Saturday, and still missing on 3,4,5,& 6. So I went thru all of the ignition wires to make sure they were all correct - they were and the plugs were firing (out of the engine).
Here's comes the interesting part. One of the checks in the manual for troubleshooting is to rev the engine to 4000 quickly, three or four times and then check the plugs. Wet would indicate getting fuel. Mine were dry but black with loose soot. I would read that as rich but firing. The interesting part is that I checked the old plugs and 3,4,5,& 6 were dark brown or black, like thay had been running rich for a while, and 1,2,7 & 8 were nice and clean - like they came from a different engine. In case you are thinking coil, I forget which is which but 3,4,5, & 6 share both coils.
One more hint - every time I've done something, she will start and run very smoothly for between one and two minutes, and then start missing.
Any ideas? Please help!!