teb91

You may want to do a resistance check of the coils when they are hot. For months I had an intermittent stall, bucking at speed, check engine light with no code, and like yours it would run fine for a few days even a week or so. Finally threw a code for all 4 oxygen sensors. Only common for both banks is ignition and each coil fire plugs on both sides. Found the left coil had resistance of 16ohms when hot where normal is 10-14. Changed the coil and its been fine for 4 weeks now. This is a 92 SC400, hope this helps.