Hello --

I recently started experiencing a problem with my 2002 Toyota 4Runner (168k miles) where it is making a metallic rattling sound on acceleration. It literally stops when you let off the gas... but as soon as you so much as touch the gas it returns. It sounds like it's coming from the passenger side of the engine compartment. I have run 87 octane for as long as I've owned the truck and just filled up w/ 93 in the hope that it might help. The sound is still there.. albeit perhaps slightly less so.

The first time I noticed this was a month ago but it went away within a minute and hasn't come back until now... where it is constant.

How would you diagnose this / what would you guys recommend here? I'm not sure if this is called a "knock" or "pinging"... but it is very concerning!

Thanks in advance!
-Steve

Baffle inside one of your cats?

replace your catalytic convertor.... i just replaced my original muffler at 272,000 miles.... i can here my cat now.... next paycheck

I had a similar problem right after I bought my '02 TR4. I was probably around 70,000 miles at the time. It was a very light rattling, only on acceleration. After taking it back to them twice, they told me it was some kind of heat shield. They fixed it...for the time being. 160,000 miles later...the sound has returned! No more warranty, and I don't live near the dealership that fixed it the first time.

Good ideas, guys! I will definitely try to get a better feel for where the sound is coming from exactly. Do you think it could be pinging / detonation? I am considering Seafoaming the engine {it has never been done} in the hope that this could help should it be pinging.

Does it rattle when you step on the gas in neutral or just when it has a load?

OP, based on your comments and those in this thread it could be any number of things and no clear way to determine what it is exactly ...

My money is on a leaky exhaust ... cheap welds break over time. I had a similar issue and it was a exhaust leak.

Take it to a muffler shop or Toyota place (not a dealer) for diagnosis. Don't just pull your cats based on this problem description.

On further inspection (my neighbor's ears while a step on the gas) it does not seem to be an internal engine issue but instead a rattling heat shield somewhere on the exhaust path. It does go silent when you let off the gas, but has a distinctively metallic sound. I am going to put the truck up on ramps and inspect the path back... I bet you guys are right that it's a bad weld along the way...

Thanks for the great advice here! I am relieved that it doesn't seem to be pinging/detonation. I'm also crossing my fingers that it isn't internal to one of the cats!

the bolts on one of your heat shields probably rusted out. I had the exact same problem. It is a quick and easy fix, just put a new bolt on it.

That's what I was saying!! Post back if you figure out what it is so I can get mine fixed!! The rattles drive me crazy!

I'm having the same issue, its between roughly 2 and 3k rpms, and most noticeable under load, like accelerateintng or pulling hills or using the engine compression to slow down... I hope its not the back "y" pipe heat shield, cause if it is I'm not wanting to pull the motor, and I don't see a way to get to it with out pulling the motor. If I have to pull the motor in just gonna put a set of headers on...

Does it sound like this...

https://www.youtube.com/watch?v=A9i8EYTsRrM

I get this sound at 2000 and 2500 rpm...
Happens at
:20
:29
:38

yeup, its more of a resonance vibration that a rattling sound. i dont think its my muffler, as its not coming from the back of the vehicle. it to me sounds like either the cat is lose(but i have no CEL) or in the engine bay

got the same problem here, seemed like it got worse within the past month. i just cant pin point where exactly the rattle is coming from????????

Yep, mine has been doing that for about the last 7000 miles. Not getting worse just worrisome at first. Nothing I can find loose under the truck and can't spot any exhaust leaks. I'm assuming it's the guts of the cat working loose. On one of my 95s it finally broke loose and rattled like crazy - you could hear it coming down the road. I don't remember it starting out this way but it probably did.

If anyone figures it out let us all know.