Knock at idle
- Thread starter 02-Sport
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I really don't believe it has gotten any worse. I remember coming home from college years ago and went to drive the 4runner when my dad still had it as one of his spare cars. The noise was present so I have no idea how it started. I thought maybe the dealer did something when they changed the timing belt. Since all this started I have had the injectors tested (they were perfect), new crankshaft pulley, new o2 sensors, new timing belt with all idlers and pump, mew plugs and wires and checked, MAF cleaned, IAC cleaned. One theory I have is that is could be the flexplate. It seems to be coming from down low in the engine. I was having trouble getting the inspection cover off the transmission so I haven't looked into that yet.
BlackCat914
New member
No, knock sensors only detect pre-detonation.
BlackCat914
New member
Is it lower engine noise? If so, I'd throw some 15w-40 oil in it and see if it stops knocking. It won't hurt it to have thick oil in it for a bit while you're diagnosing the noise.
PitbullRescuer
New member
My thought was a noisy valve train and considering your mileage, it would've been a good place to start. Until you said it goes away in park and neutral. My guess is that it's a flex plate issue. Pull the inspection cover off, give it a good look. Not a bad idea to have a friend rotate the crank bolt (Clockwise only) while you're under there. Grab a good flash light, it's tough to see up in there.
the_antihero
New member
Thread revival.. Has anyone confirmed the cause and/or the solution to this problem? I just bought an 02 2WD w/ 188K. I didn't realize it at the time of purchase 
out: The knocking sound only manifests itself in gear at idle, but disappears in neutral or park. The truck drives fine but I can't help but think that this is a sign of something unhealthy going on. I've brought the truck to a very reputable T4R shop in San Diego and they couldn't find the problem, and dismissed it as a one of those mysterious benign things that happen to high mileage T4R's. I've also searched online and found some blaming a cracked flexplate. The shop checked it through the access panel with a camera and found no crack. I've found some older threads online pertaining to the same issue, with no solution or updates posted..
Weird knocking sound - YotaTech Forums
http://www.toyota-4runner.org/3rd-gen-t4rs/88875-knocking-noise-when-gear.html
99 3.4L 4runner ticking sound...need help. - YotaTech Forums
http://www.toyota-4runner.org/3rd-g...er-sport-ticking-sound-when-gear-stopped.html
'99 SR5 unusual knock/thud sound... need help pls - Toyota 4Runner Forum - Toyota 4Runner Enthusiasts Forum
out: The knocking sound only manifests itself in gear at idle, but disappears in neutral or park. The truck drives fine but I can't help but think that this is a sign of something unhealthy going on. I've brought the truck to a very reputable T4R shop in San Diego and they couldn't find the problem, and dismissed it as a one of those mysterious benign things that happen to high mileage T4R's. I've also searched online and found some blaming a cracked flexplate. The shop checked it through the access panel with a camera and found no crack. I've found some older threads online pertaining to the same issue, with no solution or updates posted.. Weird knocking sound - YotaTech Forums
http://www.toyota-4runner.org/3rd-gen-t4rs/88875-knocking-noise-when-gear.html
99 3.4L 4runner ticking sound...need help. - YotaTech Forums
http://www.toyota-4runner.org/3rd-g...er-sport-ticking-sound-when-gear-stopped.html
'99 SR5 unusual knock/thud sound... need help pls - Toyota 4Runner Forum - Toyota 4Runner Enthusiasts Forum
I have had two trucks start this knock at idle while I have had them. One was a 1999 Tacoma that started at 150,000 miles. The other has been a 2002 4runner that started at 209,000. I think it has something to do with sub par gas being run through this things. Sticky lifters and a dirty valve train .Seafoam worked for me. I put a whole can in gas tank and a 1/3 of a can in the oil. I then put 1 2/3 cans through the vacuum line. I ran the seafoam in the oil for about 300 miles. After the seafoam treatment I started buying lucus fuel additive in the gallon form. I love this stuff. You can hear a huge difference in the valve train. Buy the little bottles of lucus and just fill them from the gallon jug. Its pretty cheap.I'm using it I all my vehicle's on every fill up. I swear I feel like it runs better and better. I love these engines, but their fuel systems need cleaning too. That is what stopped the knocking on my 4runner. Or go get a motovac treatment.
the_antihero
New member
Thanks, I'll try the seafoam but it really doesn't sound like a valve train issue.. it's more of a knocking than it is a ticking. The engine idles smooth and quiet when there is no load in park and neutral.
What is torque converter knock? and what is the "front pump" on the trans?
Well, hope you have better luck than me. My knock occurred with load, then would get quiet with out (idle or de-accel). Compression was down some in #5 cylinder but still 120 when warm vs 135 _ on others. Not valves, spark, flexplate.
I took it to master tech who said it was a crank bearing. They all checked good. I finally took the head off. The #5 bore was marked up. Pulled the piston, the upper ring was jammed in and had metal smeared across. It was piston slap (ie loose piston). I got a used engine that I am in the middle of swapping. The old engine actually had enough diameter left to clean up with honing, but I choose a replacement engine.
My old engine was 96 4runner at 290k miles.
I run syn oil every 6k miles. But at last oil change I stuck in castrol high milage conventional. Within 100 miles the knock became noticeable. Thicker oil, engine honey had no real effect.
Let me know if you have any questions. I just finished plugging a tire on the Sienna. SO time to clean up.
I took it to master tech who said it was a crank bearing. They all checked good. I finally took the head off. The #5 bore was marked up. Pulled the piston, the upper ring was jammed in and had metal smeared across. It was piston slap (ie loose piston). I got a used engine that I am in the middle of swapping. The old engine actually had enough diameter left to clean up with honing, but I choose a replacement engine.
My old engine was 96 4runner at 290k miles.
I run syn oil every 6k miles. But at last oil change I stuck in castrol high milage conventional. Within 100 miles the knock became noticeable. Thicker oil, engine honey had no real effect.
Let me know if you have any questions. I just finished plugging a tire on the Sienna. SO time to clean up.
the_antihero
New member
Did the knock disappear upon acceleration? (mine does) It only occurs at idle, and either in Drive or Reverse. It is quiet and smooth in neutral/park/acceleration. Did you experience any loss of power, check engine light, blow by, smoke from the tail pipe? I really suspect that it's a trans related issue. I am having the shop take a second look at it. Perhaps a compression check is in order.
I see, thanks for the explanation. I hope the shop is as good as the reviews say they are, and are able to get to the bottom of it.
On my 96 4runner 3.4 with the bad piston, the noise was very noticeable while under load, not there on de-accelerating. So maybe there is hope for yours.
BTW, I did try taking the bolts out of my flex plate to tq. Just push the tq back a little. It did not make a difference in the noise, eliminating the flex plate, tq and tranny as possible issues.
BTW, I did try taking the bolts out of my flex plate to tq. Just push the tq back a little. It did not make a difference in the noise, eliminating the flex plate, tq and tranny as possible issues.
