Hi, 99celcior here. I drive a 99 ls400 and Bin having a rough idle lately, the car seems to drive fine but at idle I could feel a little bit of a shake I went ahead and did a tune-up on the Car. spark plugs and coil on spark plug boots. Changed my motor mounts found out they were cracked. change the transmission mount. Still had a rough idle so then I change the ocv solenoids with no change. Thought I had bad gas so I ran the tank empty and refueled ran injector cleaner through it. No check engine lights are on I look for vacuum leaks, no leaks. Still rough. if anyone out there has any ideas let me know, thank you

 

is it rough only in D, or when it's in N too? in neutral it should be idling at 750 rpm, and 500 rpm when in drive. a dirty throttle body can cause a low idle that won't be as smooth.

 

I is rough in park, nutral, and drive. I cleaned a little carbon out of the throttle body. still didn't help. also cleaned mass air sensor.

 

Sounds like the blockage of air mix passages. Those can't be cleaned simply. You need a full can of cleaner or more and a good air compressor. The link below may help you to understand how you use a compressor.
https://www.clublexus.com/forums/ls-...w-ac-on-3.html

 

I will try and clean the ports above the tb and
see if it works

 

So I cleaned the tb today and before I started, i wrote down the fuel trims. both banks long term was -4% at idle, and -0.5 around 2k rpms... after a can of tb cleaner and blowing commpresed air through the 2 ports on top tb... rough idle is still there but long term fuel trims are different .
idle..
bank1= -3.2
bank2=-0.8

2k rpms
bank 1=-0.8
bank2=2.3
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I'm thinking I need to clean some more. the rough idle seems to be a little better but still there. if any one has an idea on this please let me know thanks

 

Is your check engine light on? Does it feel like the car wants to cut off? have you tried cleaning the MAF sensor?

 

I cleaned the maf. one of the first thing I did. no light on. drives good just rough
bump in idle when not moving

 

OEM idle for a 98-00 iirc is 650rpm +/- 100rpm ONLY MEASURED IN NEUTRAL OR PARK. Measuring in drive is NOT correct. Measuring with the AC On is NOT correct.