First off thanks to any yota fan that can send a little info. my way. I bought my truck a couple weeks ago as is with 232,000 miles, timing belt kit and waterpump changed at 220,000 miles. The engine is making a rattle or knock in the top part of the engine at idle, pretty loud, if you push the accelerator it will dissapear and start again at idle sometimes sounding quieter. Motor is not missing and has great power, no smoke, oil is clean. Any help would be greatly appreciated, thanks in advance.

 

it could be any number of things... seals on pistons.. broken piston.. it may be getting to be that rebiuld time.... :/ but its hard for me to diagnose without seeing and hearing...

 

Probly the large idler for the cam belt.The one the upper rad hose hook to.As you can immagine it gets hot.
Bigblock

 

Difficult to diagnose is it a rattle like a diesel or more of a ticking sound?
mine was ticking from the valve lifters I put a can of "Engine Restorer" in at oil change and it quieted right out almost immediately did it again at next change and it's been quiet since [3 changes]. I also switched from Mobil1 5W30 to the 10W30 grade.
The ER stuff comes in a silver and black can and sells for around $20 for the 6cyl. size can.

 

Thanks for the input gentlemen. Aviator this is noise is loud, more like diesel than ticking. Bigblocks idea of the cam belt idler might be on the money. It sounds quieter one minute and noisier the next. Oil pressure is great. If the noise was in the bottom part of the motor I would think rod bearing. This is on the top of the motor more in front than rear just at idle. Again thank you guys. This is the best Toyota site on the web!!!!!!!!

 

If the "ticking" goes away when the RPM's are increased it could be your vacuum switching valve, i recently had a very loud "tick" at idle which i believed to be coming from the engine, but closer inspection revealed what was actually causing the noise. although, thats on a 3.4L which is near the rear, i think it might be on the front passenger side on the 3.0L if i remember correctly.

 

Sounds like a broken motor mount. Like when its idling it is slapping against it, and when you give it gas it has even steady pressure. Had this happen on my bro's jeep before. Good luck!