Atrofee

When the car is idling the Tach is below Zero by nearly an Inch, Although standing still Speedo below zero close to an inch too. While driving Tach behaves normally during shifting but shows about 800 range. Police officer says I was doing 79 in a 40. Spedo said 40. Tires are 255/35X20s
Wheels are recent but behaved same with stock.
Thanks

Atrofee

Update:
I spent some time on a IT Helpdesk where I would visit the users desk for a large company. When I would show up I would ask what the problem was. The reply would always start with the words "All of a sudden". I call these visits "Stump the magician" I then explain that I do not document reasons why or anything. I just repair however I need for you to tell me if you added any software, no penalties. Im later told of this screen saver or widget they like. It helps diagnose things. The LS with the instrument issue is just that. I do not own the car

First Problem:
The Tach went below zero then became inaccurate

Second Problem:
Putting Tranny into drive would drop in with a BANG

Third Problem occurs with Traany Bang:
Speedometer goes below zero and is of by 20 MPH

My thought is the Tach has sticking needle issue and the Tranny/Speedo is trunk wiring harness. I will keep everyone informed of this pls add input if you think Im on the right track
Thanks

cobalt91

Both the tach and speedo being off makes me think someone has has had the instrument cluster apart. I think there is a thread on resetting both.

mspearl95

you couldn't tell you were doing twice the posted speed limit?

Kansas

I never heard of a procedure to "reset" the tach and speedo. Just because they are inaccurate doesn't mean the cluster has been messed with. Maybe buy a portable GPS to augment your speedometer since most show your speed on the main map screen - they are also more accurate than a vehicle speedometer since they give the true speed.

I've seen a lot of threads about the trunk hinge wire issue and have had the problem myself on the 90 LS I used to have -- nothing I've ever seen indicates a connection between the trunk hinge wires breaking and a speedo/tach problem like you are having.

cobalt91

Thread: how to fix your speedo needle when it doesnt work.
This is what I think I read. Sounds like similar issue to me.

TaninAuto

Common problem with the 90-92's. Cluster needs to be completely taken apart and new (used) needle assemblies installed.

LScowboyLS

in the meantime, until you get it fixed, this FREE app from the Android app market (Google Play Store) will tell you your exact speed in giant numbers on your cell phone display.

It has saved me several times from getting a ticket and is huge so very readable while driving, there is a even heads-up display mode which uses the reflection in your window to show your speed.

this is GPS-based and FAR more accurate than your Lexus's speedometer was when new!

PureDrifter

iTrader: (10)

sorry to burst your bubble, but civilian GPS at 1HZ (which is what's found in most cell phones) is far, far less accurate than OEM speedometers.

Mil-spec GPS systems which are reliable within a few feet and operate on 10HZ or more are far more accurate, but generally are only found in aftermarket GPS transmitters.

LScowboyLS

PD, hate to burst YOUR bubble, but you have totally jumped the shark on this one!

modern cellphones use chipsets such as the SIRFstar III or IV a-GPS which are typically integrated into the snapdragon or tegra 3 chipsets

by utilizing a-GPS, (cell tower assist) even my 2 year old T-mobile G2 (HTC Desire-Z) locks on the highway in less than 1 second and with 4m accuracy, this is better than all of my Garmin nuvi standalone GPS units, and ever since Selective Availability was done away with by good old Bill Clinton, back in the year 2000, civilian and mil-spec are now the same spec.

maybe some really cheap phones have crummy GPS, but better Android phones and even the iPhone 4s will typically ace a nice standalone GPS unit (due to a-GPS), and TROUNCE the speedo in your car, that can be thrown off considerably by something as seemingly insignificant as the difference in diameter of a worn set of tires vs. a new set.

Kansas

Let's give PD a pass on this one. He's almost always right about everything else.

PureDrifter

iTrader: (10)

actually not quite.

A-GPS is practically worthless in terms of gauging speed, and is used primarily to aid initial GPS position lock. 4M accuracy is consumer grade, as there is still a difference in military spec and consumer spec devices (such as ionospheric correction, which will eventually trickle down). there's multiple reasons GPS devices arent used in any product cars to gauge speed or distance other than for navigation purposes, including inaccuracy and inconsistency.

standalone GPS can have A-GPS, and higher end devices can be VERY accurate (the G-box is a great example, and relevant).

the speed derived from a GPS signal is a calculated number, the one in your car is based on a physical relationship, and when working properly is exceedingly accurate.

Kansas

Car speedometers are increasingly driven by electronic signals without a physical connection to the transmission - i.e. also displaying a "calculated number". Car speedometers always display a speed faster than actual - it is a DOT requirement. I've long noticed that our portable GPS devices read 2-3 mph slower than our car speedometers and match the speeds displayed by those mobile roadside devices that show actual car speeds.

The accuracy of GPS on Android devices is truely amazing. Just last night I happened to look our house on Google satelite view running on Android Ice Creme Sandwich on Samsung. Our house has an unusually large footprint with roof variations that make it easy to tell exactly what is underneath each portion of the roof when viewed from overhead.

As I sat on the living roof sofa, the tiny glowing dot on Google satelite view showed precisely where I was sitting. OK, maybe it was off two or three feet. It's freaking amazing how far this technology has come.

PureDrifter

iTrader: (10)

for that instant it measured, it's reasonably accurate, though doesnt take elevation change in less-than-perfectly mapped areas, as well as numerous other factors into consideration, but 1HZ (cell phone standard) is a LOT of play/lag between measurements considering the OEM speed sensor measures at something like 10 or 20HZ, sometimes more.

We've gotten off-topic enough here though, this isnt a thread on the talking points of a GPS speed sensor so I'm going to quite posting on that topic now.