When I start my car...1 out of every 4 starts it makes this loud clacking sound..you hear it twice and the motor fails to start...if I hold the key in the start position while its clacking it sometimes struggles to start and it starts and runs fine..And sometimes when it clacks it just dies but will start up immediately after fine..anyone know what could be making that clacking sound? The motor shakes when it does this..the car drives fine though.

 

you could have spark jumping/grounding out, OR, something on that order.... probably not starter related.

 

That sounds flywheel related to me, like a loose or missing bolt. You could take off the inspection plate from the tranny and check (tighten) all the flywheel bolts. You'll be able to spin the flywheel with a big screwdriver or a 22mm socket on the crank pulley bolt.
Or, is it possible you have a bad motor mount and the engine jumps having the fan hit the fan shroud? Check the motor mounts by starting the car, put it in drive, keep foot on brake firmly, hit the gas a tiny bit and see if the engine jumps, also try with reverse.

 

mine also makes a clacking noise like that on cold starts for some reason but it never struggles to start.... could a spark jumping really make that loud of a noise?

 

I doubt its a spark plug...or flywheel because the car runs like brand new when started..never struggles or sputters ever. Only on random starts it makes this clacking noise..its always 2 clacks too. My friend insists that its the starter not turning or maybe has a broken or worn down teeth. When it clacks and fails to start u can hear the starter whining but not turning over the car..maybe it is the starter...who knows..its embarrassing sometimes cus the clacking is so loud..

 

tried the motor mount test..the motor moves but not much..ive had a broken motor mount on an rsx before and the ls4 motor does not move anywhere as much as the rsx did..so i dont think its the motor mount.

 

It's hard to diagnose a noise going by someones words b/c your "clack" can be someone elses "clunk". Is it possible your starter bolts are loose, maybe the starter moves? Also, I know on some GM cars they use different size shims to adjust the angle of the starter, Idk if Lexus has them.

 

Well it could be a clunk..I notice the engine does shake when it happens..maybe the accessory belt is slipping? I thought it could be the tbelt slipping but then it would cause the engine to missfire all the time which it doesn't.

 

I dont know, I've never heard your sound... but if you have spark jumping, it will affect the performance and make it run rough and die (at times) and if the spark goes on to the plug, it will run properly.

we are not trying to fix your problems, just point you in a direction so you can locate it.....
cheers.

 

I'm sure its not a spark jumping..and I'm sure the timing belt is not slipping either..it sounds like a combustion miss fire on start up then it runs fine..

 

then you need to seek professional help,

 

As stated above it's hard to tell from one persons explanation, rec taking it to a tech to have a listen and advise...

 

Sounds l ike youi are missing some teeth on your flywheel from this description. Hard to say without getting in there and gathering evidence though.

 

Mine's been doing this on occasion as well. I just assumed the above explanation was my problem. I'm not going to do anything about it for now. If you want more help from this forum why not upload a video of the noise from you starting it.........

Here's my description of what I hear.

Deetdeetdeetdeetdeetdeetdeet,...KICcicic

 

Well it happens without warning and not all the time..I'd have to record the sound from outside of the car while someone starts it everytime..its a hassle to do that lol...what would cause missing flywheel teeth?