williamJ

There is no need to replace the springs unless they have 'sagged' If your ride height is good then the springs are fine. Actually they are just dampers (aka shocks).

I had knocking noises 6 months ago and it took a while to track it down. Turned out to be the drive plate - which is attached to the torque converter so it may be the same for you. Link to the thread has a bit more detail. My link

Plug leads do occasionally break down and moisture can cause the high tension to track to earth, causing a misfire. Coils do also occasionally go bad but it isn't common with denso gear. On my 99 GS 300 each of the 3 coils serves 2 cylinders so a bad coil would affect both and the do usually (but not always) fail entirely. It would be very noticeable. My leads have done 145,000 miles and are still good. My Denso plugs have done 90,000 and are still doing well but it is really time for new ones. I wouldn't replace plugs with anything other than Denso or NGK (I use NGK for my race engines). I wouldn't replace the coils unless they were proven to be faulty. As for the leads....high quality aftermarket silicone leads appear to be as good as OEM and usually a lot less expensive. They must be top quality ones from a reputable manufacturer. I don't have a distributor cap but OEM would be best.

Well I took it to a local transmission shop that had a recommendation - I really didn't like the idea of trying to get the box out without a lift and a workshop. They replaced the flex plate / drive plate which was cracked 8/10ths of the way around the outside of the crankshaft bolts. Bolts had not come loose. Torque converter was fine. It was very noisy on the day I drove it to the shop but it hung together just long enough. The shop charged $500 labour. It is once again a pleasure to drive. While I was checking the rest of the engine over I took out the spark plugs (not a 5 minute job!!) The plugs had done 90,000 miles. They were all fine. Clearances slightly larger than spec but in very good condition. I put them back - I needed the $90 to put to the gearbox work

After much research it seems this is highly likely to be a broken torque converter flex plate / drive plate, which joins the crank to the torque converter. I don't want to remove the box myself so I am having it looked at on Tuesday by a transmission shop. They say the plates are usually broken when they make a rattle but occasionally it is just loose bolts. The plate will cost $275 from Lexus if it is needed. A new torque converter costs $1600 ouch - but they tell me they are usually fine. Hope the crank isn't damaged.....

It would be great if you could add me to the list - I have a ton of work to do on mine and none of it simple! wpa_johnston@yahoo.com Many thanks.

I think I have the exact same noise. It started as a sort of squeal only when cold and much more so with the ac on. I removed the serpentine belt (so no ac, water pump, alternator or p/steering pump) and started it cold - noise still there! I changed the timing belt and tensioner but it wasn't either tensioner. Noise gradually got worse and became a very definite rattle or knock and it seemed to be coming from the middle of the engine on the left side. I saw posts about the VVTi going bad but I cannot find anything wrong there. Without a new oil control solenoid (voltage varies between 1 and 5 volts on a live test run) and VVTi gear to substitute I can't be 100% sure though. It does sound very like a detonation rattle but the knock sensor seems to be fine and the timing does seem to be wrong using a strobe. It's all very weird. I agree that rod knock seems to be a possibility but it does not follow the pattern. If its a rod knock it is intermittently one or several of them! I checked the oil pressure which seems to be within spec. I find the noise is worse when the engine is warm and much worse when the ac or fans are running. It is improved by engaging drive. That bit is really weird - how on earth would that change a rod knock? It does not appear at all when cruising low (20) or medium (70mph) speed. When I lift off the gas at 20mph it rattles briefly though. My oil consumtion is fine the valve clearances are fine, never been run low on oil or overheated. A mechanic who heard it has suggested that it could be to do with the transmission - he thinks maybe drive plate. Does anyone recognise any of this and maybe shed some light?