92LSSCOTTY

So i recently flew to san diego to pickup a 92 LS400 with 168,xxx miles. I test drove it and it felt good. drove 8 hours home and felt no issues until i noticed this one kink.
driving anything above the first gear runs like a champ, but in the lower gear driving slow like in traffic or stop sign/red light ( 3-10 mph) sometimes it randomly spikes a few hundred rpms up and down at around 600-800 rpms
I noticed this doesnt happen when cold but when warming / warmed up it does this every so often. any ideas?

Amskeptic

I would check first for a correctly adjusted throttle position switch. Does yours have the factory tell-tale yellow paint still on it? If so, leave it be and only check with a multimeter.

Second, check temp sensors. If it is good cold (richer mixture due to temp sensor) and acts up warm, it may be that the mixture is leaning out too far.

Third, oxygen sensor feedback maybe out of range. Have you run codes?
Colin

400fanboy

Are those spikes in RPM causing you car to lurch forward? Does your throttle pedal becomes sensitive and difficult to maintain control of the car when you're creeping along in those 1st gear, 5mph situations? Is it really hard to have the car smoothly accelerate after braking from a higher speed, but didn't quite come to a stop? In those situations, does it seem like no matter what you do, the throttle just doesn't want to be smooth?

If so, I suggest this to see if the more detailed symptoms makes sense to you:

https://www.clublexus.com/forums/ls-...ttle-body.html