Missing out and thwarting/ knocking sound

Been fighting a rough idle and "thwarting sound" (th th th th th th th) at idle.
2001 3.4L V6

Truck isn't throwing any codes. I have a ultra guage and I've had it scanned at autozone, still nothing.

So far I've replaced: coils, wires, cleaned MAF, fuel filter, PCV valve, plugs are 4 months old but about to get changed again.

The plugs that are in the truck now were connected to stock wires (13 years old) so I finally replace the wires 2 days ago but maybe the old wires caused too much damage to the 4 month old plugs, which is why I still don't feel a difference?

I've also Seafoamed twice within the last 10 months. The 2nd time was to try and get rid of this rough idle and thwarting sound which did nothing. The thwarting/ knocking Noise sounds like it's coming from the driver side of the engine.

One thing I have noticed is all 3 plugs on driver side of engine have "corona stain". The first time I changed the plugs was after I bought the truck 12 months ago, at that time I don't think the plugs had the corona stain on them but they were the stock denso plugs so I replaced them with NGK single electrodes.
4 months ago is when I started to feel the rough idle so I changed the plugs again but this time when I pulled the plugs I noticed the driver side plugs had the yellow/ burnt stain on the white part of the plug. Thinking that was the cause of the rough idle I replaced all 6 plugs with new NGK dual electrodes. After that I still had the rough idle but kinda ignored it up until now.
I checked the plugs yesterday and I saw the same thing on the 4 month old plugs, more corona stain on the 3 driver side spark plugs.

Is this common?

I'm gonna replace the plugs again tomorrow with denso dual electrodes. The passenger side plugs look new and always have. Other than the corona stain there isn't any other bad signs, no carbon build up or burnt electrodes.

Anyone have any ideas as to what else I can try?
Anyone think the Corona stain could be the cause?
Or maybe it's not corona stain but a different issue?
I was told it's normal but the missing out/ noise seems to be comming from the same side where the plugs keep showing up burnt on the white insulator.



Side notes: 2 things I remember getting done around the time I started to feel the rough idle and thwarting sound. First thing was I had the timing belt changed by a professional. It ran great for about a month then I started to feel the rough idle/ thwarting.
Second thing I did was seafoam the intake. With this I also remember the truck running very smooth for a while after then about a month later it started to idle rougher and make the thwarting sound. Not sure if either of these things have anything to do with the issues the truck is having but just thought it was worth mentioning.

 

By description of the noise and the rough idle......Vacuum leak? Maybe an intake leak. Maybe exhaust, but it sounds like it's just one cylinder. Spray each vacuum line/fitting with a shot of WD40 and see if the idle note changes as you go.

 

I'll definetly try the spray method. Exhaust leak was what I originally thought but when I had my catytic converters installed 3 weeks ago (and O2 Sensors) they checked for leaks and there weren't any.

 

The Th,Th sounds like a leak. The overheated plugs also sound like an intake air leak. The knock noise could be a dead cylinder. Possibly because of the leak. You could also have a bad valve. That would cause a dead cylinder and maybe a leak noise through the intake. Could be a head gasket, but start simple with the spray and good luck. Also, You could start the truck with one of the six plug wires (or coil packs unplugged) removed and see if the noise or problem gets worse or stays the same. Do them one at a time, then re attach it and pull off the next one...Each time the truck should run poorly. If you pull off one and it runs the same, You've got an issue with THAT cylinder. I think you've already identified the three that it could be.

 

For anyone who is experiencing rough idles here is some info I found out today about mine...

Took it to the professionals today and had it hooked up to a couple different machines and found out NOTHING! He said all signs are good and where they should be. Compression tests are good too. One thing he did question was me dumping the end of the exhaust just after the axle on the turndown. When I cut the exhaust a couple months back made a small cut about 5" from where I actually cut the exhaust. He says it's a possibility that the small incision at the end of the exhaust is making the sound of an exhaust leak which would explain the "th th th th th th th" sound. As for the slightly rough idle he says to try some BG through the intake and then only use premium grade fuel. I've read enough stories to believe him about both BG and good gas, just not so sure that is gonna solve the idle, but won't hurt to try.

 

UPDATE:

Rotated the thermostat so the Jiggle Valve is in the downward 6:00 position. After doing this my temps went down from 208 to 190. Truck has been running so much better and seems to have smoothed out the rough idle and Thwarting sound I was hearing.

I had the timing belt done about 10 months ago and when they replaced the thermostat they put the jiggle valve up (like most vehicles) but for our engines it has to be down. Well I do remember starting to feel the rough idle about a month after the T-belt job so seems like the engine running warmer than its used to could have been the culprit for me. I'm praying it stays running strong because it feels good to know your truck is running as it should.

for anyone experiencing a rough idle and maybe what sound like an exhaust manifold leak or knock but no codes being thrown, check the temps with an Ultra Guage or similar. If they are in the mid - high 200's then check the thermostat jiggle valve. Im now running in the low 190's!

 

I hope its cured and I wish you well. But, as a mechanic, this doesn't seem to be your issue. 208° is not overheating. The valve is a bypass for when the thermostat is closed. The orientation shouldn't matter. And a leak downstream in the exhaust wouldn't sound like one cylinder leaking. Just a constand noise.

 

That's the thing, I didn't think putting the jiggle valve up or down was going to matter but, a 20 degree difference has really brought back life into the engine, especially at takeoff. I'm not sure how or why the valve positioning would make that much of a difference but the Toyota manual states that for the 3.4L the jiggle valve should be in the 6:00 position. I've gone months always watching my ultra guage and the engine temps were always in the 204-210 range, then when I do something as simple as rotate the thermostat I'm now at 190.4 constant engine temp, maybe 192 at idle. The jiggle valve mod has made a believer outta me. Which it's not even a "mod", according to the manual it should be that way from the get go.

As for the rough idle and thwarting sound, I'm not sure how or why higher temps would cause those effects but I did start to hear them after I had the Timing belt changed which was when the stock thermostat was removed and the new one was wrongly placed back in. As for the diagnosis everything came back showing good numbers, as well as compression test. If the higher than normal engine temps didn't cause what I was feeling/ hearing then I'm not sure where to check or look.

Do you have any ideas what I should be looking for/ checking? I'm gonna go get a state inspection so I want it to pass but if there is anything wrong with the truck, especially the emissions/ exhaust, I'd hope it fails so I know I need to start doing more diagnostics.

I really appreciate your expertise and any info is greatly appreciated!