Mind-bending Rough Running...

[rtd111]

...

O2 Sensors still havent arrived, anxious to get them! :D Will update after they are installed...

Did you get OEM sensors? What is the part number?

And generally, is there a good place to get varous part numbers for this car ((91) LS400)?

[micadevcon]

...

O2 Sensors still havent arrived, anxious to get them! :D Will update after they are installed...

Did you get OEM sensors? What is the part number?

And generally, is there a good place to get varous part numbers for this car ((91) LS400)?

I got Denso 234-4211 [says TOYOTA on them] off a decent-looking seller on eBay, new. Looks identical to the old broken ones I took off and replaced with Bosch. As for part numbers, unfortunately there isnt one single place that I have found to get that info. The service manual helps a little, but its not a list or anything.

[micadevcon]

Alright, installed the O2 sensors. No change. Dang.

But, I decided to go right back to square one. I put the old Bosch Platinum 4+ plugs back in the car. Guess what?

The car idles like a dream.

BUT, now she has no power. Feels like its running on four cylinders. Acceleration is smooth if I barely touch or ease on the gas, but any sudden or sufficient [think passing or hwy on-ramp] causes it to rumble and rev w/o power.

Most cases this indicated a plugged cat con, but this car accelerated fine, even excessively with the NGK Iridium IX plugs I had in there, but now, with the plugs the car came with, its fine. So the cats cant be bad?

Is it possible the NGK's I got were just... bad?

Going to scope the plugs and see whats going on...

[93ls400walt]

Any trans. codes?

[mejojo]

What I did was to disconnect one coil at a time to see if it idled better on one set of 4 than the other set of 4.

Once I knew which distributor was feeding the "poison" cylinder(s), I took one cylinder out at a time to see if it idled more smoothly without "this one" or "that one". That got me down to one bad cylinder, and I swapped the plug and it was much better.

I can only recommend to not use Bosch Platinums...for whatever reason they didn't serve me well.

Joe

[nll714]

Wow. I just got finished reading this entire thread and Im exhausted! I give you MAJOR credit for all that you have done, examined, replaced.....not to mention the man hours and dollars spent on various parts.

I dont know *BLEEP* about fixing cars but love reading this forum for help with my LS400.

This is like a soap opera....I cant wait to see your next post. You have my sincere best wishes that your car troubles will soon be behind you. Good luck.

[mejojo]

Follow-up on mine...I had replaced a very bad plug and the car seemed to run well, but occasionally I would still get a hiccup going up an incline, so I guess I had another plug that would only fail every once in a while. So yesterday I replaced all the plugs with NGK Ix "Laser Iridium" (online order from Kragen for store pickup with 15% online discount code ONLINESAVE15) and it feels very good so far.

I don't know what's up with those Bosch's, but I'm sorry I ever bought them. On the positive side, I can now do all 8 plugs in 1:15.

Another task I took on was the "ears" on my fan shroud that allow bolting to hold it in place had broken. I bought some 2-part epoxy and glued everything back together and it seems to be working so far.

Joe

[bencho]

I also have noticed your problem #1. Sometimes I want to just gas it and putting the pedal to the floor does not encourage a downshift. It literally stays in gear and (very) slowly increases speed. I found this out when trying to merge onto a highway and almost got destroyed by a truck.

So reading through all of this, was this solved?? I got quite confused trying to read through all these terms and whatnot. That and the brake light on my passenger side closest to the license place keeps burning out. Apparently water is getting in every time it rains. I've had it sealed and replaced but to no avail. I will take a look at the wires on the trunk hinge tomorrow...

[hughes369]

where did u get ur injectors? you can check injectors by doing an ohm test between the 2 pins

What is the value to look for when checking the resistance between the two pins of the injector? Thanks for any specs you can post.

[90Duchess]

I'm having similar problems with my 90 ls400. Your problem sounds like a bad throttle position sensor, developing a dead spot at the spot where it gets the most wear, light pedal pressure. I'd test it with a multimeter to see if the resistance curve is smooth and holds steady readings.

[Puddinhead]

micadevcon did u ever fix ur problem cuz u and i are having same issues and desperately was hoping u got a solution as i have only this car and tired of dropping $$$ on a solution

[Cman99]

Anyone solved this problem??? I have a miss at idle and in gear and shakes terribly. But goes away when over 700rpm???

 

[TurbochargedBull]

I worked on my 1992 Lexus ES300 yesterday after reading this post. I investigated the possible spark issue first since it seemed the easiest to verify and I got lucky. I did a round robin with the spark plug wires and disconnected each one at a time until I reached one that upon removing it did not change the idle status. Good spark coming from the distributor but wasn't firing at the head. I pulled the boot and found what had to be a manufacturing defect with the hard plastic insulator. The spark was firing prematurely through a pin hole or crack to the port tube. Of course this means that the spark never reached the combustion chamber which resulted in a dead cylinder. This happened approximately one month after a tune up. The effect was exactly as described in previous post. Shaking at idle and slowly going away as RPM's increase. Loss of power but drivable. However I did not have a check engine light. Perhaps my bulb is also blown. Hope this helps