Thud Sound

[Doniz]

Hello to everyone

i have owned my 98 gs 400 for a year now and have enjoyed every mile i have put on it. I have also been around this and other lexus forums and can say i have benefited from the wealth of information out here. It has been a big help in getting to know the vehicle so i would like to big up everyone on here.

I have an ongoing issue that would like some help with. The vehicle has 74k miles and works fantastic but a while back i was cruising down the road doing about 35mph and let off the gas then after a few seconds when i pressed on the gas again i heard this unusual thump/thud sound comming from the engine/drivetrain area. i could and still can make it do that noise by letting of and hitting the gas pedal again. it does this every time and i would like some help in tracing this problem if anyone might know what the cause of it could be.

thanks

[intakerGS]

There might be some 'freeplay' in an engine/drivetrain component, worn studs, loose battery etc, moving back and forth when accelerating. I assume you might have figured this out yourself too ;)

If you can't pinpoint the cause, best advice is to take it in for a check to prevent worse. I guess it shouldn't be too hard to find, as it's easily reproduced at will.

[Doniz]

Thanks i am getting close to biting the bullet and taking it to be checked out but i am pretty handy with tools and like to fix things myself unless it is something major then i let the pros handle it. I would like to at least know what it is first.

i have checked the drive shaft and things look ok no torn bushing and the trans mount looks ok too but the damn engine mount is enclosed and hard to check if faulty or not. i don't seem to have the symptoms of bad mounts - low rough idle.

but i don't know. thanks

[intakerGS]

I've driven a car (manual transmision ) with bad mounts, where the shifter would move between particular gears as well exessive driveline lash, but no rough idle. I (cheaply) fixed it by jacking up the motor and fill the mounts with polyurethane, but I wouldn't recommend.

Try revving the motor in neutral for unusual movement, although this won't always give away bad mounts. From the symptoms you describe and also considering the age of the car, the mounts are suspect.

[Doniz]

Thanks i suspect the motor mounts also but on this car it isn't easy to check them out its covered pretty well and the engine doesnt move about when i rev it, even when i put it in gear and give it some gas it doesn't have any unusual movement

[TRDGS300]

hmmm... does the noise happen only when the car is moving? if not, start the car and pop the hood. play with the throttle(rev it up lightly) and see if you can hear the noise. if not, your motor should be fine, then its probably something loose. as mentioned above could be a battery, motor mount etc...