My GS300 has developed a rattle on start up. Sounded more like a rough bearing at first, so I removed the auxiliary belt and ran it. It was less obvious but still there - so I renewed the cambelt and tensioner. No improvement at all.

Noise has got a bit worse and is consistent on start up - very like a diesel. But if I put it into Drive, the noise goes away. If I rev it the noise also goes away. After it has been driven a short way the noise is hardly there at all in Neutral, but if I switch on the A/C at idle it makes the noise. Is also tends to make the noise when the cooling fans come on at idle. When I'm driving the noise goes away entirely except when I am off the throttle and nearly at a stop.

I start trawling the net and lots of posts about VVTi cam gears going faulty. I don't really want to spend£££ only to find it's not that so I have looked at the oil control valve - seems okay (moves freely) and solenoid operates with power supply. The filter in the oil line had a bit of dirt in it but wasn't blocked.

Someone suggested that there was problem with the valve clearances - if that is so then how can they suddenly improve when Drive is engaged? If it's momentary oil starvation then how does that happen? The noise location is hard to pinpoint - louder on the left side of the engine and seems to come from the middle to rear of the head area. I have wirted a voltmeter to the Oil Control Solenoid and it shows between 3 and 5 volts most of the time - dips to less than 1 volt when I lift off the throttle. Does not change at idle when I go from Neutral to Drive but the noise goes. Before I did a road test on the voltage I gave it 12 volts at idle - the motor stalled instantly!

Which is it? VVTi gear; Oil Control Valve and Solenoid; Oil supply to the valve; Oil supply to the head; Something else entirely?

Any ideas much appreciated.

Bill

Anyone..........?

Maybe I'll have to give in and go to the dealer, which would be a shame (and very expensive).

Is there any information out there about how to test the solenoid or the oil control valve, if I could elimante those then it would point towards the VVTi gear assembly perhaps?

Any advice welcome.

It was NOT a noisy top end!!! Turned out it was the torque converter drive plate (flex plate). The noise got gradually worse and the source appeared to move rearwards.

The plate was replaced last week - new plate £170 plus labour £350 plus vat (not Lexus). There was a crack almost all the way round just outside the crank bolt holes. Still seems wrong that it should rattle like a top end or bottom end or piston but it did.

Hope this helps someone else to diagnose their rattle and knock.

[quote name='WilliamJ' timestamp='1283898445' post='731664']
It was NOT a noisy top end!!! Turned out it was the torque converter drive plate (flex plate). The noise got gradually worse and the source appeared to move rearwards.

The plate was replaced last week - new plate £170 plus labour £350 plus vat (not Lexus). There was a crack almost all the way round just outside the crank bolt holes. Still seems wrong that it should rattle like a top end or bottom end or piston but it did.

Hope this helps someone else to diagnose their rattle and knock.
[/quote]

Hello William,
I have just joined the forum and would like some advice if possible. I hope this is the way to use the forum!
My 2005 Lexus GS300 with 56,000 miles (genuine)has occasionally a loud rattle on starting from cold. This may happen for a few days and then vanish for quite a while. I have recorded the noise but my Lexus garage could not offer an explanation. I wonder how you found that the torque converter drive plate was the problem and any ideas where else to look in the forums.
Thanks,
Oldun