ericw10

Is CEL light on? If so go dump the codes. If the knock sensor is working it could be sending an error which might be a clue. If not it could be a faulty knock sensor. If the ECU doesn;t get feedback of a knocking condition it might make improper fuel/timing decisions since it isn't seeing the knocks.

I would search this forum regarding knock sensor and see what you come up with.

Thanks for the reply. Nope, no CEL or any other error. But may just have to take it in to have it scanned for codes. Will probably be $100 just to hook it up, at least will have an idea where to start looking.

I have '90 LS400 with 197K miles. Engine runs great with excellent power, good smooth idle, and no other problems that I am aware of. But about a month ago, it started to have a pretty significant knock when accelerating from a stop for only the first second or two, then quiet. I mean it will knock/ping from idle to about 1.5-1.8K RPM, then nothing. I can be on the freeway and nail it full throttle and it just goes like hell and smooth/quiet as can be.

We use nothing but the highest octane grade available in California (91) and I have run several polyether amine based fuel system cleaners through it (RedLine and Gumout Regane)but no difference in the knock/ping at low RPM. I had a muffler shop check the EGR pipe to see if it is cracked or leaking and he said no.

Any of you veteran LS gurus have any ideas? I was hoping for a simple fix but doesn't look like it's going to be the case here.

Bleeding just entails turning the wheel left to right numerous times, while the engine is running. You may even find a short drive doing figure eights will help.

But by changing the fluid to the correct stuff you may have uncovered a problem that was already existing, the ATF is a thinner, lighter fluid so if you had a leak it's more prominent now.

That's what I feared, that the new synthetic fluid was now doing its job by cleaning out the accumulated varnish etc and maybe clogged the solonoid and/or reservoir screen. Now its running in high pressure mode all the time, but when things heat up, viscosity drops, pressure reduced and no noise. Guess I will be pulling out a solonoid screen tonight. Oh joy.

No leaks that I can see. I bought a drip pan 3 days ago and have had the car park on it every night and no sign of ATF anywhere...................yet.

I have a 1990 Lexus Ls 400, and when it is cold the pump whines really loud. Any suggestions?

I just bought a 1990 LS400 and was going through the fluids. I changed the P/S ATF to a synthetic Mobil1 Dextron III. Worked fine for several days, but then began to whine only in the morning when cold. After things warm up, it quiets right down. Steering effort seems OK. I don't see any evidence of leaks either. Did I get air in there because I have tried the left to right bit and no help.

Is there a thread on how to "bleed" the hydraulic system of air? I searched but didnt see it.

this sounds like the same issue I have.

Ask your daughter if she had to brake hard or from speed...

I'm about to chage the disks (rotors) as the heavy LS heats them up a lot under harsh braking and the natural tendency with an auto is to hold your foot on the brake once you stop, this creates a localised heat spot under the pads where the heat can't escape and warps the disc in this spot.

It's no guarantee but as discs are cheap ish and easy to change it's an easy try to just fit new ones (would go for pads too).

Yep, its a heavy beast and they undersized the brakes a little. But I don't feel any pulsation while braking indicating warpage. I just hope its not a torque converter or drivetrain issue. Too bad since up until 2 weeks ago, I would have driven this car across the USA with no worries. Now I'm not so sure. We're only into it $2500 and it's such a clean car, but if it turns out to be anything serious, away it goes.

We've had our '90 LS400 for about 3 months. It has 212K on it and very clean. Co-worker had it for 12 years and all records kept. Car drove perfectly smooth until about 2 weeks ago when we lent it to our daughter for a day. She never mentioned anything happening, but I now notice a bit of vibe and slight shake on the highway around 60-70. Took it in for re-balace/rotate, and alignment 2 days ago.

Tech said alignment was out "quite a bit" but now in spec, so I thought that would have solved it, but it has not. Inspection/rotation did not indicate any bent wheels, worn parts, etc. These tire shops make their living finding things to replace, so if suspension/steering parts were bad, I'm sure they would have made me aware.

No unusual sounds at all and the trans shifts fine. Any ideas where to look next? Thanks in advance.