I recently purchased a used 94 ls400 with about 83k miles, I am currently experiencing this problem where the RPM on idle is around 600 but on accelerating it drops to zero and I have loss of power. Initially the car would not even go faster than 20mph, but after a day or so I was able to get it to 70mph. There is a loud humming sound from the engine and the engine is knocking at times. I am wondering if there is anyone out there that has similiar problems. Thanks

 

There have been several discussions with these similar symptoms. Could be your ignition coils going bad. More detail for the symptoms would be appreciated for us to help you with an answer.

 

There were no symptoms leading up to the problem, I remember it being cool outside and the days before i did notice some faint burning smell coming from the vent but did not pay any more attention. Any clue as to what i need to look for?

 

glowing cats...no not ur neighbors kitty

 

Where is the ignition coil, and how hard would it be to change it? I think that might be the case because i suspect that i might be only running on 4 cylinders only so maybe only one side has gone bad and the other side is enabling me to continue running but no acceleration.

 

There are 2 of them. 1 is on the passenger side of the engine, right on the very top at the end of the head (very easy to change). The other is on the driver side, down deep on the side of the engine itself. Look between the battery and the lower half of the engine itself and it should be the only thing with what looks like a spark plug wire coming from it. This side can be a real PITA to change, but is possible with some patience.

Borrowed this pic from new guy, SeriousLS, for illustration. Hope he doesn't mind me using it.

 

spent half of day waiting at the local firestone as they changed my cat converter, heard the clanking sound and thought that migh solve my problem as well as the heat coming from underneath the car. not sure whether driving around the last couple of days with this problem caused my cat to crack or break. anyhow didn't solve my problem, car still hesitates and no power. wasted $550!@#
Anyhow, want to try the ignition coil option but
i found 2 different types at autozone a duralast and beck arnley, any idea which one is better? would appreciate if there was some tutorial on changin both.

 

It turn out that ignition coil was bad, got it fixed today. thanks trukn1

 

No problem,, may want to consider changing the other one as well. 1 goes bad,, matter of time b4 the other will go as well. When I did mine, i just went ahead and did them both to get it out of the way.

 

Thanks for reminder, i changed both.