3.4L V6
1999 4Skinner
65,000mi
no maintenance history except recent 5W30 oil change

First of all, I know what rod knock sounds like, and I know what low octane valve rattle sounds like, and I dont have either one, but I have this 'knocking tick' or a 'knocking rattle' that happens only at idle and you cant hear it when accelerating from idle. Here are all the characteristics:
(1) Occurs intermittenly
(2) Only audible at idle
(3) Sometimes slightly louder than others
(4) Always goes away when shifted from drive to N or P
(5) Sometimes happens when A/C is on and in D
(6) Sometimes happens when A/C is off and in D
(7) Always goes away when A/C is turned off

It seems like when the A/C is turned off or when shifted from D to N it takes a slight load off the engine and makes it go away. I am 30 years old and dont have the best of hearing as my ears ring pretty loud so I am not even going to guess where the noise is coming from.

I have an Asian friend that is a very good mechanic, I described it to him and he said its probably either a bad harmonic balancer or a collapsing timing belt tensioner.

What do you guys think?


I just bought this vehicle from a Lexus dealership that was a local trade-in. It is a 1999 3.4L V6 4Runner with 65,000mi on it. Before I bought the vehicle I asked for a compression test, but they didnt get the compression test to me untill after I had already purchased it. Here is what they sent me via email as far as the compression test:

DRY:
90 80
100 98
80 80
He said he did the “wet” test and it was normal.

I am not sure what the corresponding cylinder numbers are, but should the variations in pressures be alarming? My Mitchell's CD states that the pressure should be at least 150, a far cry from the dry test of 80-100. I hate that they didnt give me the numbers for the wet test. Comments?

Thanks guys.

 

those compression numbers look awfully low to me. It would make sense about the harmonic balancer or timing belt tensioner. Does that motor have a seperate idler pulley for the ac belt? If so, I would definately check that. For a quick test I would just take the a/c belt off and make sure that the problem has gone away, that way you can pinpoin the problem easier.

 

[I]I know what low octane valve rattle sounds like[/I]

Ain't no such thing!

What you may be hearing is preignition knock. The knock sensor in the engine should take care of this. If your engine is set up for 92 octane gasoline and you're running standard 87, that's probably what you should expect!

There is no such thing as "low octane valve rattle"!

 

Low octane valve rattle was a poor choice of words - what I meant to say was low octane valve pinging.

BTW, the owners manual reccommends 87 octane.

 

If those are actually the numbers, that engine is toast (or it could also be the timing belt has slipped significantly since that is intergral with making proper compression)......but those are so low I have a feeling someone didn't do the test right. You might want to have it brought in and compression tested professionally somewhere else. In any case have somone do the compression test again. If you get numbers below 150 psi then start checking the timing marks on the cam and crank pulleys (you need to pull off the timing cover to do so).

 

You could just do the compression test yourself. Make sure the engine is at operating temp and with the throttle wide open, do the test. Your numbers should be way higher. You wont hear pre-ignition at idle, at least I never have. Only under load. Look for loose components or your ac system for the noise.