ac680

I have this 1991 LS400. (76K miles but who knows..)
Bought it very very cheaply because of a very serious misfire.
I am a good mechanic, mainly diagnose, and repair electrical problems on late model Mercedes, MBW's Jaguars and an ocassional American made car.
I do not fix much Japanese, seems the quality control is better but sometimes I see problems because of bad repairs.

Anyhow, I have this big early lexus, no check engine light, idles very very nice, no noises, shifts well, I did replace plugs, wires and caps, and coils because of water in the plug tubes. ( steam cleaning by a dealer).
However on acceleration, and rpm over 3000 a very very serious misfire devellopes. It is not like one cylinder, it seems to affect a few, and randomly drops 3 to 400 RPM when misfiring.
I have seen this kind of agressive misfire before, usually caused by a broken intake valve spring, or serious misalignment of a distributor cap, or some signal issue with the crank pickup.
However again, no check engine light.

some input please?

Henri.

Lexushead

Maybe this has to do with Mass air flow sensor. Do a search on Mass air flow sensor.

PVSLS400

could be a coil pack. one for each side of motor

jdmaristo

Same thing happened to me with my civic SI after cleaning the engine, some water got into the cylinder head and misfired when i drove, so i replaced the spark plugs and dryed out the cylinder heads and problem went away.