m8554

I recently purchased a nice 95 LS400 with 106000 miles. The origional owner had all the service records that were done at the dealer from day one. It seems he had the same problem I am having. This happens more when the car is cold.

At about 40 mph and up under easy acceleration, everything is fine unless you have to suddenly let up on the gas. If you do this, the car "bucks" instead of a smooth de-acceleration.

The origional owner complained to the dealer more than once on this problem since the car was new. The dealer replace the ECU and changed the transmission fluid.

After the car is driven about 20 minutes, the problem seems to cure itself.

The only other issue with the car that may be related is it seems to run rich when first started in the morning, you can smell the richness in the exhaust gases.

This car has been meticulously maintained at the dealer and since it seems they can't figure it out, I thought I would check here if anyone has had the same problem.

Thanks

Mike

stock300

I had the same problem with my wife's '95 LS400 with 94,000 miles after we purchased it. I went ahead and put in new distributor caps and rotor buttons (not fun) and removed the throttle body for cleaning. Once the TB was off, it was easier to adjust the TPS and throttle stop screw. A shop manual comes in very handy. The problem went away. I'm not sure if it was the change in distributor caps, etc., or the TPS but my guess would be the TPS (Throttle Position Sensor). I've since also changed my plugs and installed a new set of plug wires (OEM). As you pointed out, the problem was more pronounced in cold weather and when the engine was still cold. I'd cruise at 40 mph and when I quickly released the throttle, the car would "buck".

johnw

I have a '95 with 115,000 miles and I had the same problem, the service manager and the mechanic at Lexus who I've known for 10 years both said it's called "Shock-lock". It basically entailed replacing 3 computer boards which cost about $ 3200.00+-. I had a major tune-up, new timing chain and replaced the power steering pump and they comp'd the boards at no cost (see some of my old posts to get more details).

Considering the cost I would sure try Stock300s idea first.

Johnw.

lextek

Throttle off shock is the condition and it was remedied by changing spark plugs and engine ecu if memory serves me correctly. (I'm juggling with engine ecu and some other ecu for some reason)

The car would actually stall in worst case scenarios, its been 5-8 yrs since ive dealt with that concern so im a bit fuzzy on it.

Just tell the dealer you believe you have "throttle off shock", if the service consulatant acts lost, ask to speak with a technician or diagnostic specialist that has been around since the intro of the 95 LS400.

Regards,
lextek

Lvangundy

This might be a more common issue than you guys might think.

It happens on the first generation cars, and I have been trying to explain this to many people. Seems like people have a confused look on their face because either I can't explain it, or they don't know, or never have driven my car!

I asked a member here about this and he said it might have to do with the torque convertor (T/C) locking up or slipping. It is ESPECIALLY noticeable when you leave the car in 2nd or 3rd gear accelerate then let off the gas. The car decelerates for a second, then clunks forward / engine brakes under the 1800RPM mark at a hard rate.

It does this on the freeway even in 4th gear and it is VERY annoying. Let's say you drive to 65mph then ease the thottle or take your foot off of it. When you want to accelerate again, you can push on the gas pedal slightly (leaving in the same position the entire time) and nothing happens for about 2 seconds. The RPM's slowly start to move up until the transmission or throttle body (whateever it is!?) catches up and the car beings to move forward.


I'm thinking it's the T/C. I had the TPS replaced not too long ago, but it wasn't adjusted to factory spec. I should try that first and see what happens.

lextek

Rear end slop in the 89-90-91 models is not unheard of by any means. Sounds like your experiencing this.

Lvangundy

Hmm.. Can you give another explanation of rear end slop?

Also, another way to explain what I described is to say the engine braking kicks in in lower gears more often than I think it should, in higher gears (3,4) it slips either into 3rd or the T/C does something funny.

My differential has TONS of freeplay. You can spin the wheel about 1/4 turn before you see the drife shaft rotate. I tried this on an SC and I barely moved it and saw rotation in the drive shaft.

hyperopt

Was the opposing wheel off the ground (free to rotate) when you perform this test? If it was, you test was invalid.

Lvangundy

Why would this have to do with having both wheels off the ground?

I tested the exact same thing on an SC300 (i know NOT a 400) on a rack and moving the wheel one direction an inch or so caused the drive shaft to spin.

My car like I mentioned will move 3 inches on the wheel before the drive shaft beings to spin.

Is this a sign of a worn differential? something? Why is the SC so much 'tighter' than the LS?


BTW - Sorry m8554 if it seems like I'm stealing the show from your thread..

500amg

'95 LS400 with 52,000 miles and I have the exact same problem. Dealer cleaned out throttle body and it did nothing. Is there any danger to not getting this fixed...? I would rather not spend ~3200.

m8554

I'm also leaning towards the "do nothing" fix for this problem after reading your (much appreciated) comments and past experiences with this problem. Its nice to know I'm not alone. I have had the car about two months now and have learned to live with the problem by easing off the throttle when slowing down. This overcomes the bucking problem which occurs when suddenly releasing the gas.

Since my records show this problem has existed since the car was new, and still exists, I see no reason to worry about it causing any damage. I now have 107,000 miles and other than this problem the car still rides as smooth as silk.

Still, I wish I could find a cheap fix for it as I guess I'm pretty picky about annoying stuff like this.

Thanks for all your input. Looking forward to hearing more.

Mike

BrianV

Same problem here for the record.

wolver1ne

I've found my '91 ls400 doing the same thing and discovered what it was in the dark...
between the radiator and front the drivers side of the engine, you'll see a wire to the distributorless ignition coil. check it at night with the car running... if it sparks ...you got to replace that wire...

TomWahjudi

So, mine does it also. I thought it only happens when the ECT mode is set to Sport. Oh well, I'll try changing rotor/cap/plug wires/plugs and TB cleaning and see if those will fix the symptom. I also have a spare ECU laying around that I'd like to try.

m8554

Please let me know if you cure the problem