I have Lexus GS300 1998 model. There are two complaints with the car.
1) The Engine runs smooth in Idling for some time & suddenly the RPM drops for 3-4 seconds and the engine shakes & again the vehicle is normal. 2) When you accelerate uniformly the engine vibrates a lot. This symptom is not there during fast acceleration.
There is no DTC recorded.
Checked the vacuum pipes- found Ok
Replaced the HT cables.
Replaced the Spark plugs.