I have a 1992 ls 400 i have been searching for a while trying to figure out where to go next. so here is the issue im having. it runs fine when im just driving to work and back its once the engine gets completely warmed up that I have any issues. once its warmed up for a few minutes it will idle very rough going up and down and will die after just a few minutes. It will also sake back and forth when I press the gasi think that's about it. I only got one code out of it and that was for intake air temp sensor and it was still under warranty from last time so I changed it. I drove around for close to an hour trying to get it to act up and nothing. but then a week later it started again only wont hold a code. so far in the last 6 months ive changed the alternator, both ignition coils, spark plug wires, spark plugs, mass air flow, fuel filter, and I cleaned the idle air control valve. I think that's all. but if any one could help it would be greatly appreciated.

 

try this: https://www.clublexus.com/forums/ls4...ange-pics.html

 

is there any way to test and see if that is indeed my issue?

 

sure if you work at Lexus and have all their testing equipment...
but I couldn't tell you how... but this is a cheap fix, do a search on it and get yourself educated on these cars... lot of help on here.... NOBODY can accurately tell you what to FIX by reading your post.

 

I know its hard to educate threw a post I was hoping someone with a repair manual would have a resistance of the sensor. I guess its just wishful thinking. thank you for your help

 

I know I keep saying this, but it's proven to be effective a number of times. If you've not changed out your capacitors per the 'all my crazy Lexus issues solved', then I suggest you do that to keep yourself from going crazy. You've been swapping out parts to no avail...this is a known problem area that can cause any number of unexplainable problems... Fix these first, then see what you've got.

 

That sensor is not too costly and if its pretty old its a good idea to replace it. The bad ones I have seen is not so much the resistance values but the connections turn to junk as it gets a bit crusty and can crumble away.
You could be having a vacuum leak and or the egr could be part of the problem.

 

So quick update I changed the coolant temperature sensor yesterday. It took it a little longer to act up and when it did act up the idle was steady. As long as I kept it above about 3500 RPMs it would act fine. But it did regain some of its pep until it acted up.

 

I would say to check the MAF sensor but you already stated that you changed it. I would really check all the rubber vacuum hoses AND clamps. Sometimes the clamps are so old that they don't give a proper seal and the houses have a lot of carbon built up in them that the engine can't breathe.

 

So then it will not idle correctly?

 

When the car is warmed up, check the coolant temp via a scan tool. I had this happen on my '96. The ECM was bad and was showing the temp to be 80 degrees when the car was almost 200. This caused the computer to pump way too much fuel (like a choke) into the engine thinking it was still cold. The problem was the source voltage that is supposed to be 5V to the coolant temp sensor was way off.

To test this get the car hot, shut it off, unplug the coolant temp sensor on top of the engine and start it again. Unplugging it will place a default temp of I think 180 degrees IIRC and it would run great then.

 

It didn't used to idle fine when it was warmed up but after I changed the coolant sensor it will idle fine.

 

I had issues with my 1991 LS 400 with heat the car would stall and shutter the head tech at a Lexus dealer told me to change the TPS throttle positioning sensor and no more problems. First I changed the temp sensor nothing now when changed out the TPS the car runs some much better and plenty of power. This could be your problem when you change TPS it has to be adjusted with a scanner that sets the TPS for maximum performance...

 

so quick update I pluged off the egr valve because some one suggested that to me. and its still doing the same thing but just not as bad its kind frustrating. I have adjusted the tps to idle at 650 ish if there is a better way to adjust please let me know. a link could be helpful

 

This is just a reply back from the original assumption that the connector was at fault. I ended up replacing both variable valve timing (VVT) sensors and found the connector was part of the problem too. I still have a code - I believe it's lean on bank 1 but is been a min. The car doesnt idle funny anymore so I'm living with it till I get motivated to work through that next.

They sell them on Amazon for like 60/ea I believe so I'm happy with that.