08 4runner V6 engine rattle noise

I have a 08 4r v6 210,000 has a rattling noise coming from the front drivers side of the engine, only after the engine is warmed up, and only at idle.

 

Like rattling a can of spray paint? Or more like a steady knocking?

 

Kind of, intermittently bring the RPM to 1,200 and it goes away.

 

Sounds like the normal 4.0 knock to me. At idle there’s a very noticeable knocking and will go away if you slightly rev up the engine. Then it returns gradually as it idles back down to 500RPM. Every 4.0 Toyota I’ve seen does it, I had a 2011 4Runner and it did the same thing. It almost sounds like a very small diesel engine.

 

I was wondering if it could be the A/C clutch?

 

I don’t think it engages unless you have it on. I could be wrong, but I only hear it click on when I have the AC turned on. The 4.0’s are notorious for having a unique knock to them, kind of like valves needing adjustment but a little louder and more profound.

 

So, I'm not alone? I took it to my friend (runs an auto service), he put his "Electric Ear" on it and said that it sounded like a valve adj.

 

Its hard to know exactly what you’re hearing based on text description, but yes the 4.0 engines have a very distinct knocking to them that is not abnormal to my knowledge. I’m not an expert on the mechanics of the engine though, so I’d trust your friend as he’ll be able to give you a better diagnostic than someone on this forum.

 

Thanks!

 

Finally figured it out, it's the Alternator, dealer replaced it back in Sept.