Hi, trying to troubleshoot my dads '98 LS400.
It's only started recently where once the car has warmed up, his coolant temp gauge will drop intermittently. Then when the car comes to a stop at a light, the car will sometimes (not always) stall and won't start until 10 or 15 minutes later. If the coolant temp gauge stays normal, the car won't stall.

I've tried changing the thermostat, but the first time I took it for a drive afterward, the coolant gauge was pinned at C, even after 10 minutes of idling and a 5 minute drive. When I slowed down and nearly came to a stop, the car stalled. Had to wait 5 minutes before the car would start again. Any ideas as to what the issue could be?

 

Sounds like a coolant temp sensor or ECU related issue. I would check the voltage at the coolant temp gauge first.

 

Change your ECT and check for corrosion on the ECT harness.

 

I was going to change the coolant temp sensor at the same time and had actually bought one with the thermostat, but the only writeup I found for it was for a '95, and the engine bay looks pretty different from my dad's '98. I'm not too familiar around the Lexus engine bay, so I couldn't pinpoint where the sensor was actually located. This is the thread I used as a reference:

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

Do I have to take the cluster apart to check the voltage at the coolant temp gauge? I'm not too familiar with Lexus.

What's an ECT? Is that the same as the ECU?

 

engine coolant temperature sender.

 

Is there a separate writeup for the '98 somewhere, or are they similar enough that I could go off the one for the '95? I know the engine bay does look slightly different.

 

'98-00 info is present in the big thread.