So I drove my car to work and every worked properly. but when I got off of work.. and started my 96 ls400.. the engine revs up and down on its own until I put it into drive. to be honest its kinda of scary it's like 3/4 throttle to 4k rpms and then drops to 0 at the same rate and then repeats.. it feels controlled and calculated and even timed??? BUT its never done this before!!! is it safe to drive? did i hurt my car? how do i fix this? DAMMMMIT!

 

Let me know if you’re still looking for the solution I might be able to help you out

 

If you know what it is then just post it. That's why he asked the question, for a solution. Plus, alot more people would want to see an answer if they read this thread, and others like it, in the future, like 5-10 years from now.

 

and those people you mention, 5-10 years in the future will be looking for the right answer, not some answer I gave on the minimal information I have from the poster. What good what it have done if I had said “Hey replace this 300 dollar part and let’s HOPE it fixes your issue” not to mention that, that 300 dollars for that part could be the only cash on the side OP has to spare I know because I’ve been there.

 

I'd check the coolant level, rpm hunting like that can be caused by the coolant temp sensor running in air. Up to 4k rpms seems bit high though.

 

I thought maybe you had an idea what it might be from your past experiences. This happened to a buddy of mine's 97 LS400.
His symptom could be one of many different things. Alot of people look for "suggestions" on what it could be that they could check themselves and rule things out.

I'm letting you know, we're all looking for a solution. Are you able to help us out, with any suggestions?

 

As you stated previously there is quite a few different things that it could be, typically for something like this I would say clean out the throttle body but for our cars (early 1997 and below) *I own a ‘96* There’s an electrical issue, specifically with the ECU, Toyota-Lexus used a cheaper component for their capacitors in the ECU which would eventually lead to basically acid leaking onto your board, I have some pictures of my ECU for reference if you’d like to see. However when this happens it can cause maybe 1 or 2 issues or even the whole list of problems associated with this issue. That was why I was trying to get a little more information from OP, because their problem is *similar to a symptom on these cars, easy and quick replacement and you can also check it pretty easily you just need a deep socket 10, and a small neck chunky phillips head, take out your gloveboxes and the ECU will be on the right side, with the 10 Mils holding it in, after you remove it to check inside use the exact same Philips head and unscrew the part of the ECU that says “1UZ-FE” and then proceed to unscrew all the Philips on the edge of the board you can see, once removed GENTLY GENTLY lift from the top of the board *which is the side where the connections to the ECU enter into the unit* there’s two ribbon cables at the bottom you do not want to break those, but you should be able to see everything you need peeking in through the top, the capacitor is just a little brown and grey cylinder that sticks out of the board examine around it, if it has failed you will most likely see acid around the capacitor and corrosion on its connections into the board keep in mind that there are multiple (for example my ‘96 has 6 capacitors but other model years have more or less) and you may not see it right away. I hope this helps everyone.
Edit: After replacing the ECU you should notice a number of improvements as well such as improved fuel economy, more engine power, and smoother shifting especially from 1st to 2nd

 

It is true that those QAS capacitors are the must to be replaced when aged.

But sorry to say that some of what you have mentioned were not quite correct. Those QAS capaciors are more expensive than other electrolytic capaciｔors at that time. Toyota never used cheaper capacitors. They were selected intending to have better performances especially at colder places such as in Alaska and they had to choose QAS capacitors since those showed very good performances even at low temperature at that time of the design.

Another one is the liquid. It is not acid but strong alkali.

Toyota does not use Phillips screws but uses JIS screws.