Rattle at Low RPMs around 1200-1800

[timjamz]

Hello, all! New owner of a used 2007 base sedan with manual transmission, about 130K miles on a replacement 1NZ-FE engine.

I am getting a rattle in the top of the motor (pretty sure timing side), at low RPMs around 1200-1800. It happens under load (i.e. clutched and accelerating) or revving free, but more noticeably under load. The rattle does not happen at startup like a typical loose chain slap. RPMs do not fluctuate abnormally. Idle is good, but perhaps a little low around 500 and shakes ever so slightly. I have done the following:

- Replaced spark plugs with the recommended Denso iridiums.
- Cleaned the VVT solenoid and screen (both were in good shape but cleaned anyway).
- Cleaned the PCV valve (I did notice it does not close all the way sitting loose, but it does have *some* spring tension and blocks air only one way as it should).
- Changed the oil with Valvoline synthetic 5W-30.
- Added octane booster and filled up with 93 octane.
- Flushed the clutch line (and whole brake system) with new DOT3.

Still the rattle persists as described.

Googling and ChatGPT suggests the VVT solenoid may still be failing, the chain tensioner could be failing (why did they move it inside the timing cover on this model?? ), or the VVT sprocket could be failing. It also suggests exhaust or similar rattle due to worn motor mounts as a possibility, but that seems unlikely to me and doesn't sound like it.

Before I throw parts at it, do you all have any experience with this issue? I don't mind replacing the VVT solenoid and PCV valve, if those could be the culprit(s).

Thanks for any feedback or advice! I would love to get 300K+ out of this engine, and the vehicle is otherwise in great shape and drives super smooth.

[NYC-SE]

Are you absolutely sure its coming from the engine? I ask because similar questions have been asked before and quite often it turns out to be a loose exhaust shield. The rivets rust out and it starts to vibrate, often RPM dependent. I've had that happen to me and at first I couldn't figure out where it was coming from but after consulting this forum I noticed "exhaust shield rattle" coming up again and again. Just bent the shield a little and the noise stopped. That's all I got for you, if its anything else you're on your own. Good luck.

[timjamz]

Thanks, NYC! Well, in life can we really be sure of anything? Kidding aside, I did reach back by the firewall and tug and push on the exhaust shield covering the manifold and it's solidly attached. If there are other shields to check, I have not lifted the vehicle enough to crawl so far under as to check the exhaust all the way to the back. I may do that this weekend, just to rule things out.

It definitely sounds to me like it's coming from the engine bay at the top timing side. When I say "rattle," I guess what I mean is it sounds like a knock, but quieter. It is in time with the RPMs, not like a vibration. The noise is somewhere in the middle between valves tapping and a rod knocking, but I have enough DIY repair experience to be rather confident it's not either of those.

I appreciate the feedback!!

[timjamz]

Just thought I would update. The rattle disappeared after I worked on the AC system. It was at basically zero pressure, so I replaced the seals and valve cores (schrader valves), pulled vacuum, and recharged the system. Whether it was the empty compressor rattling (not sure how since it was not engaged) or I happened to secure something in the process of working on AC lines that was rattling before, I'm not sure.

Happy to report, I have nice cold AC now! :)

[NYC-SE]

Two birds, one stone.

Glad you got it sorted out.