Exhaustgases

If its in good shape and you love it, then don't give up on it. To do the code test you don't start the car to do it. To bypass the relay and resistor you use that same paper clip and jump from Fp to B+ in that data port on the driverside top front of the engine, you reach behind and kinda pull up on the little greyish brownish lid and it hinges forward, look down inside the little lid for the location of the terminals. And you do need to make sure it has good fuel pressure first. Next check for spark. Also these cars have the ecu capacitor issue, and its not too big a deal to fix or have it fixed. Fixing a good car is better than wasting money on some other crappy brand. You kinda jumped to fast on replacing the fuel pump, though running them dry is not a good thing. If you do the bypass then the fuel pump should run all the time the ignition switch is turned on. Other things that aren't going to let it start are things like the igniter, cam or crank sensors, wires to these items and the connectors. And maybe you thought it ran outa gas when it was really one of those sensors. Sensors can be intermittent. And then yeah it could be fuel related, fuel system and even bad gas with water in it. There are just allot of bases to cover to figure it out. The thing about trying to figure it out is don't get fixated on one thing that you think it is, it maybe completely unrelated to what you think it is. I'd say before anything you need a DMM and they are very cheap or free at harbor freight. First check the battery connections and the battery voltage. Make sure all the terminals of the fusible links have power 12 ish volts with engine off. Make sure all fuses are good. This is the starting point. Then move on to the fuel pressure, its hard to check because you need to connect to the fuel rail with a gauge, and do that bypass to make the fuel pump run. The fuel pump won't keep running unless it sees an rpm signal that lets it know the engine is running, and that is why they have the ability to bypass to check for pump operation. Then check for spark and the spark plugs.

http://www.lexls.com/tutorials/intro/codereading.html Yeah a nice smallish paper clip will do, no big fat wires in those little plugs. The older LS's have a built in code reader of sorts.

Yes there are. Some pretty expensive scan tools can do OBD1. And here is how to do it at home with no code reader, and it works just fine. And just use a smallish paper clip not a huge wire like in the photo. There is a data port on the engine also that has the correct terminals to jump. http://www.lexls.com/tutorials/intro/codereading.html

I was going to ask how did he know what to replace the burnt one with ?

You will need a manual and a schematic for that year car. And can get it at the Toyota site. And start at looking at fuses and relays. And it could be the switches are dirty or corroded some.

There is NO cleaning the air meter on the 1990 to 1994 LS400's. Its a Karmen vortex type unit, and a cleaning attempt will ruin it. They may be able to be cleaned if they are completely disassembled so you can access the mirror to clean it. But then the calibration maybe ruined.

The things it can be are. And they are NOT in any special order here. A leaky fuel injector, leaky cold start valve, ignition system misfire (caused by bad spark plugs, wires, cap, rotor etc. even the ecu or the ignitor) too much fuel pressure, worn out O2 sensors, bad or weak ECT (Engine Coolant Temp sensor) Do not attempt to clean the airmeter / mass airflow sensor, that will ruin it. If it was me, the things I would replace, that is if they have not been replaced in many years are one the O2 sensors, and two the ECT. And normal tune up stuff like spark plugs, checking the wires and other ignition components. And yes before just jumping in on that try to figure out what is happening first. A check of fuel pressure with pump on and off will tell one the pressure and then if the system holds the pressure for a bit, if not then possible injector leak.

Craig, is it the same deal on the 98 or do you also have an older LS?

Its not a competition or a race to do something like a starter replacement. Its better to spend 2 days or more and do it right than goof things up trying to rush it. Even the so called professional mechanics mess up (actually allot) from trying to speed through a job. It could be that the gears are meshing too tight, the bendix clutch is not working right. So does it make gear noise when cranking the engine? It may just clear up with use too. And meeee toooo always test a starter before installing especially a very difficult install like the LS. I also did my LS like Landar did, do the double test, one on the floor, the other right after its bolted on. "Not as bad as expecting" ??? It must be different on that year. Its a very nasty job on a Generation 1, the crispy electrical connectors are what makes it just bad. And the rear coolant cross over manifold and the wire loom. And the next to zero clearance between the engine and firewall, it would probably be less trouble to take the engine out to do it.

Very nice color. Something is wrong the steering wheel is on the passenger side. I wonder if there has ever been a pilot and copilot type LS400 with dual controls?

My first guess is crank position sensor.

Alternator is suspect / voltage regulator. Also make sure the battery connections are good. And remember where the cables connect to the clamps can get corroded as well. Verify the alternator is putting out the correct voltage. I had a similar problem it was the battery connections. Also make sure battery is in good shape.

The control will back off the gas going down hill but if the hill is real steep it will over come the engines ability to hold back the cars speed. LS cruise control at least on the Gen 1's does not control the brake system, maybe on the newer stuff its different I don't know. It would have been easy for them to tie it into the ABS system kind of like the Trac system is. And Lexus could have done that on the very first car in the Lexus line up. It would have been nice. And actually it is likely all in place in a Trac system car to do it with just a software modification. Too bad they don't release software info for the old stuff, its so old school why would they give a rats _____. With a gen 1 to incorporate the cruise control into the ABS, the Cruise control ECU would have to be able to communicate with the ABS ECU, and unlike most all the now modern cars that have intercommunication with all control modules, the old Gen's did not have that. The older Gens though have the ABS and Engine ECU in communication with each other at least on the Trac systems cars.

I have a 90 with that same problem, I have not dealt with it yet. But I know the problem is with the key lock assembly and the switch there in. I don't know what happens to it, it could be both a corrosion issue and an out of an adjustment deal, like I say I haven't fooled with it yet. I have worked on the trunk lock though but that was dealing with stuck tumblers and such. If I remember the switch just removed from that assembly. And major problem with Lexus parts and even other cars they will not just sell you what you need, they have it all in a nice expensive assembly. Even things like power steering return hoses, you don't just get the little rubber one you need you get the steel pipe as well. So its not a position sensor its more of just a switch since a position sensor is most always a variable resistor. I will check my manual and see what it is for sure if you need more info. Oh and the courtesy door open close switches are most always the cause of the alarm going off when the car is just sitting, like at 2 am and waking up all your neighbors. I suppose the hood switch is part of that deal too.

A good reason why DIY isn't always a cheap route to go. There is no reason any of this should have happened, a real tech would not have done it. And for all wana bee's your car is not the place to learn any sort of mechanics.

Post a sound video of it idling, I'll know if it is right or not. With what you say about the highway speed rpm, that is not the correct rpms so the tachometer is not reading correctly. Most all tach's I am familiar with use the ignition pulse signal, and since the engine runs you have that just fine. It could be a wire or connector problem, and could be a circuit problem in the tachometer electrical components. It could be similar to the ecu capacitor problem and just a bad capacitor on the tachometer circuit board. And so cool you got the idle surge sorted out. There have been a lot of LS owners with that problem and no resolution yet, well you solved it. Good work. You have done things that some so called auto mechanics can't do. Heres a tach problem

And the fluid is at correct level? It could be seal rings I have seen them be heat related. When the problem happens a pressure check would tell a lot.

If it starts and dies its not seeing an rpm signal. You may have either cam or crank sensor or ecu problem. With no signal ecu opens the circuit opening relay.

Maybe the tachometer is wrong, it maybe idling faster than it says. The engine would barely keep running at such a low speed. It is not uncommon for these tachs to do that, Tanin autoelectric knows the fix for that.

http://www.lexussouthatlantaparts.com/showAssembly.aspx?ukey_assembly=795408&ukey_make=1082&ukey_model=15669&modelYear=1991&ukey_category=21750&ukey_trimLevel=19107 scroll down to 17650

So have you applied to be a tech at your local Lexus dealership? You have probably accomplished more than most of the auto techs could. If you want to improve your solder skills just get some old junk computer parts and experiment with them first. At the rate you are going soon you will be able to open your own repair shop, keep up the good work. And don't take such a long vacation from these lexus sites. You have done some very impressive things. Just remember there are lots of stories of people taking their cars to a shop and spending thousands and they never get it fixed. So you really have beat some of the shops out there with what you have done.

Grandson should have bought an old junker. The 90 LS400 should have been put in a huge sealed box.

Tell them you will take 6k and let them have it and find another one. I'd say hunt around and copy some high priced ones to prove what the cost is if they total it.

It could be the fluid is low, it could be there is an oring for the screen that is not sealing. A leak will at a point cause the fluid to be too low. It could be a tc drain back valve is leaking, because of clean fluid. I am more with the low fluid and or sucking some air O ring deal. Fluid at operating temp, level car, and engine running at idle in park to check the fluid level.

At the top of the egr valve unit there is a diaphragm with a port and a small hose follow it, it goes to the vsv. No volts on the vsv connects ports E to F and would open the egr. With 12v it then connects port E to the filter and that would close the egr. Sometimes there is carbon build up in the larger bottom hose at some where in it that goes the egr modulator that is the thing that has 3 small hoses on it and ports labeled P R Q at the top and one larger hose at the bottom.