1999 ls400 Tachometer reads at or below the first line on the tachometer, and at times almost flatline in drive while stopped,
Scan tool reading indicates 517 RPM in Drive while stopped...this may seem low, but am running a 4.3 liter 3UZ-FE transplant, so the 1UZ-FE ECU could be compensating.
MAF sensor is new Dealer part. New throttle body position sensor, but accelerator position sensor is original.
Steering vacuum switch increases RPM about 50-60 RPM when turning steering wheel and AC Compressor operation increases idle speed further.
This could be an issue of a tired circuit board component.
Anyone successfully tackle this one?

 

When I bought my 57,000 mile LS400, the tach needle must never have gone above 2,700 rpm in its life. It was owned by an old man and then it sat for years, in a garage thankfully. On the road, my first punch-it-passing move stuck the tachometer at 2,700 rpm for the next few miles until I tapped the top of the dash, then it sank down well below the "0".

I disassembled the instrument cluster at the next gas stop, and manually moved the needle to successively greater rpm positions and looked to see where it would rest when I let go. Eventually, I got to 8,000 rpm and felt the needle slip on the shaft a bit, and there was "0". It behaved for the rest of the cross-country drive. But, I knew calibration was in my future.

With A/C on, in Park, all of my LS400s normally show a 750 rpm idle, and it drops down to 700 in drive with A/C. I was reading about 50 rpm slow until I did my superglue operation (here on the forum in some thread) to repair the speedometer needle. Once again, I rotated the tach needle carefully to that subtle stop point somewhere around 8,000 rpm, and I went 1/2 mark further. Tach then rested slightly above "0", but my indicated idle rpm is now as above other cars.
Colin