I have a 2006 Honda Civic Sport. It has a VTC activator rattle. As far as I know, it is due to VTC losing pressure and the pin coming open. When it cold starts, it rattles until the all pressure is built.
Basically, those systems get full of crud a lot of times. First, take all the parts off the outside. Clean out the valve assembly and the filter screen.
Sometimes it is as simple as one of the gaskets leaking oil and you replace the gasket when you take it off, or the screen is all clogged up and needs cleaning.
A lot of times, that will do it. Make sure you are using good-quality oil. Change the oil filter and a lot of times that will fix the rattle. Now, if it doesn't, it is actually physically in the actuation system and that costs a lot of money if it stops. Once it starts firing, you better live with it because you will have to rebuild the whole engine. You'll spend a fortune to fix that. You can have your rattling engine inspected by a professional, such as one from YourMechanic. They will be able to diagnose the car and let you know what can be done to resolve this issue.
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