For the longest time, my truck was idling a little on the rough side, with a little bit of a knock to it...

Went away for a couple days after changing the spark plugs...

It seems to idle at about 650 - 700 RPM... I'm not sure it still makes the funny noise when you bring up the RPMS any higher... The fan is kind of overpowering, lol.

I'm kinda lost, since it ran great for a couple days...

 

Hmmm...I wonder if you have a carbon build-up.
How did the plugs look..oil foulded?
Is the knock from the bottom or the top of the engine and is it constant, or just on acceleration or on decelleration?

 

I can only hear it on idle... From the drivers seat that's the only time you can hear it...

The plugs did have a fair amount of blackness on the flat round surface in the combustion chamber , however the electrode and where it arcs to weren't fouled in any way...

I'm not sure where the knock is coming from, I'm assuming from the middle of the engine and up, lol.

It stopped for a few days after I changed the plugs... Maybe she's just running a little rich for idle... I'll see if I can snag a soundclip of it or something...

 

Update:

The knock only happens when it drops to about 600 - 700 RPM and lower.... It does not happen any RPM higher than that...

It also seems to only happen when the engine is warmed up...

 

is it a loud knock or soft knock does it sound like a metal to metal knock and since its only at idle i wonder if its pinging and not knocking im thinking i may know what it is but not sure just a guess im wondering if its your lifters or valves chattering just a guess though someone may have something better

 

Well, it's not a loud noise overall... Could be pinging, I suppose, lol.

But like I said, it disappears soon as it gets back up to the normal 900RPM or so (which has to be done manually, once it's been warmed up enough, the RPM's drop).

I think it's the low RPM making it knock/ping and such...

 

k does it seem more like a mechanical type of fix or something that can be helped by using higher grade gas and maybe even a fuel system cleaner another thing you can try is lucas oil stabilizer it takes a while to put in but it makes a difference see if any of that might help i know one of the others on the forum may have a better solution im just adding options that don't cost alot. hope it helps

 

Well, we'll see what an oil change nets me... It's been about 5000 or so km, so it's about due... Hopefully that'll help...

Gonna be getting a new fuel filter and air filter, too...

 

cool yea when you do the oil if you decide to go with the lucas it replaces exactly one quart of oil so instead of 4.5 quarts you would just by 4 quarts and get one bottle of lucas put the lucas in first cause the oil you put in after will help it curcilate better and get in the system faster plus then you willhave a half a quart left of regular oil so another thing too is for the lucas they have two types one for regular oil and one for synthetic the black label is for synthetic and the other is for regular let us know when you change your oil if it helps it helped mine alot ran cooler and better after i did it.

 

As this seems to be an engine performance issue, I fail to see how an oil stabilizer will help... As a rule of thumb, I stay away from the "meracle in a bottle" type products that are in for the duration.

Anyway, Dennis, when was the last time you did an upper intake cleaning? It may be time for one. I know I'll be doing the smoke show the next time I do an oil change on my Rainier and that only has 28k miles on it. Go grab yourself a bottle of Seafoam and run it through the throttle body. Since you just replaced your plugs, you shouldn't have any problem with them. Do the seafoam right before you change your oil. Warm up the engine. Remove the intake duct work, unplug the MAF sensor. Dribble 2/3rds of a bottle down through the throttle body with the engine running and your hand on the throttle to keep it running. With the last 1/3rd of a bottle, pour it in and let the engine stall. If it doesn't stall, have someone there to shut off the engine a short bit after you pour the last in. Don't worry, you won't damage the engine. Let it sit for a good 1/2 hour then drive it like you stole it until the smoke stops coming out of the tail pipe. Change the oil and you're done.

See how that goes. It's been a long time since I have recommended this and come to think of it, with the carbon buildup problems that these engines have, this could be the cause for a lot of peoples problems!