Solent303

Hi, I'm the second owner of a 93 LS400 with around 60K miles on it. Even though the car was not used regularly, its run perfectly for all its life. Recently it developed a rough idle, engine vibrations, and sounds very different from they way it used to run. I've posted a YouTube video with sound at the exhausts.

While I'm not new to working on cars - been doing it for years as a hobby - I don't know the LS400 systems yet, and could use some help narrowing down where to focus on. I'm thinking possibly a dead coil / damaged wire... but I would think that would give a check engine light if thats the case, yes? Also CPS failure?

Here are a few additional observations:

- Lacks Power / Acceleration
- No Check Engine Light is On
- I used an IR Temp on the Exhaust Manifolds: 350-410F - was hoping to see if raw fuel was making it past the cylinder
- Its Due for a T/B job

Any thoughts on where to focus would be awesome.

http://www.youtube.com/watch?v=L2gjTyGPP_w

deanshark

Seeing how you said "I'm not new to working on cars" the basic inspection is the same. Check for spark at all 8 plugs. But then there is also the Engine Coolant Temp (ECT) sensor that you can change which will put a little more Ummph back into it. It sends some important info to the ECU. (It does wonders) Also the Air Flow Meter (AFM) is know to go bad on some of these, and sometimes doesn't throw a code. If you use the search feature at top of the page you will get an enormous amount of info and answers you need in the future. Welcome to CL.

Change ECT; https://www.clublexus.com/forums/ls4...read-this.html

Check AFM; https://www.clublexus.com/forums/sc-...on-issues.html

SkulCracka

vacumme hose leak?? maybe

jtbel

My car is a '97, so I'm not as knowledgeable about your year. First of all, it sounds kind of like when my egr pipe developed a leak. If you can get a manual, it will help you greatly. The coils can be checked with a voltmeter (check manual). Park the car somewhere at night, with no light around, with the car running check for arcing from any of the wires. Crank and cam sensors can be checked with a voltmeter also. Check to see if there is any mud on the crank sensor, mine was covered with mud and was causing problems. Not too sure, but I think your year is a non-interference engine, so worst case scenario if it breaks, is to leave you stranded. Good luck.

Solent303

Thanks for the links and suggestions guys. Plenty of things to focus on for sure. Just glad to have a focus now since so much of this engine is buried under covers. WSM is on the way to me...hopefully it has a vacuum diagram in addition to all the testing procedures for the sensors. Much Appreciated.

Solent303

Its taken a while to post a follow up, but wanted to thank you guys for pointers given. Service was very simple, and the car is running great. It passed state inspection (including emissions) with flying colors. Service items included:

• Temp Sensor - Lexus Brand
• Plug Wires - NGK Spark Plug Wire Set
• Plugs - Bosch

I'm not sure which of these was making the car run so poorly, since I did them all at once...it was easier than pulling all the covers off multiple times. I did run a few tests on the old parts though.

Temp Sensor Resistance: some readings were in line with the "resistance @ temp" required, while others weren't - so I can't place blame solely on the sensor, but it was probably on the way out, and was easy / cheap enough to change.

Plugs: Most looked good with the exception of #2 - browner and burnt residue up the white insulator.

Wires: I added my measurements below. N/C mean No Connectivity, or no reading on the multimeter. #7 clearly had an issue.

Thanks again

PureDrifter

iTrader: (10)

you had a 5cylinder for a while o.o

Solent303

Yup, good chance of it, though I wonder if the wires were brittle and broke as I pulled them off the engine. The lack of power and bad idle tells me you're probably right.