No, never did. What are we, 6 years later and about 60,000km later and no progress on this front. The noise is still there and it hasn't really changed much. The 4runner works great still.
As I mentioned, it only happens when it is warm out, when the engine is full hot and sitting at idle. In normal day to day daily driving you never really even notice it. Certainly doesn't seem to be an issue. I'm pretty obsessive about maintenance and noises, I don't think the average joe would even hear it.
Back when I first posted this in 2014 I took it to a Toyota specialist shop who have some experience with the 3rz and balance shaft deletes in particular. They listened for a bit and didn't think it was anything unusual. They said they would listen for it on the next 3rz they worked on and let me know but they never did.
I spent a fair bit of time under it with a stethescope that first year. I seem to think it comes from low down and toward the rear of the engine, maybe even bell housing. I have sort of been thinking it might be something in the clutch rattling a bit. Really hard to be sure where it originates.
Things I tried: Changing oil brands, no difference. Changed to the Tacoma mini header, no change. Valves have been checked when I first bought it and fairly recently adjusted,also no affect. I have only checked oil pressure that one time but it was great then so I have no reason to think it is any different now. The only thing that has had any affect was cleaning the AIC valve and TB. This raised the idle rpm up maybe 50 rpm and the noise is a little less pronounced. Any rpm above idle and it is gone.
I have also spent a bit of time snooping beside others with 4 cylinder tacomas and they have a pretty noisy idle too. I'm not sure mine is an isolated case, I think I am just listening for it now while others have never noticed.
In short, I am not sure it is an issue at all. Just going to keep driving it. Please let us know if you happen to find anything.
Thank you very much for your reply. Great to hear that your 3RZ is going strong.
I've looked through a number of threads on the 2RZ and 3RZ (I googled '3RZ hot idle tapping') and it seems that the issue is common, though nobody ever gets to the bottom of it.
Piston slap, wrist pin noise and balance shaft noise often come up, but only balance shaft noise would be every second turn of the crankshaft. Also, because I rebuilt my engine using only genuine parts, and had a very goodmachine shop do the rebore, I'm pretty certain that these things cannot be the cause. I have put about 50,000 km on the engine since the rebuild - so it's in that sweet spot where anything majorly wrong would have become obvious by now, whereas the new components are still (hopefully) long away from becoming worn.
The things which I did not replace that come to mind are:
-valve lifters - the valve claearances are still spot-on after 50,000 km but the lifters themselves might be worn. That said, neither myself nor a couple of experienced mechanic friends can really see how a bit of wear on a plain bucket lifter would cause a tap. What did interest me was
this review on Amazon for a new lifter. Seems at least that guy cured his problem. At the weekend I plan to run the engine with the valve cover off and see if I can find the noise.
-timing chains and tensioners / guides. Maybe i should have replaced all this, but the chains were still well within tolerance so I saw no need to replace them. I really don't see how a timing chain would make a low frequency tap. From my research, a noisy timing chain makes the engine sound like a diesel when it revs down.
-exhaust manifold - I'll take a hose to my ear and have a listen for cracks - mine is still on the original 1996 manifold - and at the joins with the downpipe. My cat is quite rusty so I'll check there too, but I never smell exhaust fumes near the engine.
-camshafts - again, given the clearances are good, I don't see a reason for a tap.
That's about it. Overall, I think I can sleep easy with this noise. If I do find it and fixit, all the better.
Thanks
EO
