I had the same thing happen to my 90 ls400. I am still baffled. My story is a little different. I finished putting a new timing belt, plugs, valve cover gaskets, power steering idle valve, distributor caps, oil crankcase seal, oil pan gasket, and new timing belt tensioner on the car. It took a long time for the car to start probably because the intense cleaning of the throttle body etc. Now when I start the car it starts fine but wont go above 2000 rpm and shudders really bad. I take it on test drives with the pedal floored and it just wont go. When I get back i see smoke and the catalytic converter is glowing red. I followed the advice for the ignition coil and replaced it but same results. One more thing, I pulled the spark plugs wires of on the drivers side while it was running and no spark. there is spark on the passenger side. that tells me that it is running on four cylinders. I need help on figuring this out.
thanks,
Lance