This is my first post here, and I have a very bizzare problem with my car. It's a 99 es 300 with 160000 km on it. For a couple of months now, the car makes a single clunk sound if I turn the engine on and get the car moving. It's more like the sound of crushing an empty can of pop by hand, but a little thicker. And it only happens once (i.e. not continous or intermittent) as the car's speed reaches 8 or 9 km/h or so, and it only lasts 1 second or so. The sound seems to come from the middle of the engine bay, in the engine/transmission/differential area, and I think the problem is in one of these 3.

The problem is very consistent, it always happens under the following conditions, and never otherwise. Also note that the clunk never occurs as long as the engine is not turned off, no matter what I do with the car's movement or the gear selector, nor is it affected by the operating temperature of the car.

Conditions for inducing clunk:

1- Engine off, car in P or N. Start engine, put car in D or R and accelerate to above 8 km/h. Single clunk sound occurs.

2- Engine off, car in P or N. Start engine, while car is on uphill/downhill. Keep car in N, and let it roll forwards or backwards until speed above 8 km/h. Clunk occurs.

3- Car is coasting in N at speed above 8 km/h. Turn engine off, then start it on again, while keeping transmissin in N. Clunk occurs

Thinking the problem might be the starter, I decided to try starting the engine without using starter. So I did this:

4- Car in D, coasting at 50 km/h. Turn engine off, then while keeping car in D, turn ignition to On position to re-start engine without using starter motor (kinda like how a manual tranny car is push started). Clunk still occurs.

So far, there doesn't seem to be any other problems with the driveability of the car. I'm somewhat knowledgeable about cars, but this problem just has me

 

Wow, this is definitely not good for your tranny. You're liable to have a lot more than a clunk if you keep that up.

Anyway, it sounds like there's some sort of speed sensitive functionality that may be malfunctioning. For instance, speed-sensing power door locks that kick in at 5 mpg in most cars. I can't recall what speed sensing functions the ES has, but there could be some sort of actuator in the engine bay that is clunking at speed. That would explain why it only happens once after you get going, as well as why it happens after you turn off the car and turn back on at speed.

Sorry, i couldn't be more help but that's the only thing i think of off the top of my head.

 

Welcome to the Club. Let me give you another idea, https://www.clublexus.com/forums/sho...d.php?t=310922

 

Tranny not shifting out of 1st properly?