[kphilpott1500]

Hey guys I'm new here and trying to figure out what could be causing my truck to have an random rough idle. Its a 2004 silverado 1500 with about 175xxx miles. Bone stock other than built 4l60e 3000 stall air raid jr kit and a black bear performance autocal tune and msd wires. Truck runs great and has no issues while driving but randomly when idling in the driveway or at fast food drive thus i get an extremely rough idle. It almost makes the truck sound like it has a huge cam in it and it shakes the entire truck when it happens. I've changed plugs and wires and a couple other things but nothing has helped. Truck throws zero codes for anything other than knock sensors. It's starting to drive me crazy and I have no idea where to look anymore! Any help is very appreciated!

 

[fpab7]

First thing that pops into my head is maybe a vacuum leak

 

[kphilpott1500]

that was my first thought to originally but it's almost to random to be that. It will idle fine 6/7 days a week and then it only acts up maybe once or twice. If my cats are stopping up could it cause a similar issue?

 

[1985zx900]

If your cats were stopped up , it would struggle to excelerate. Manifolds could get cherry red hot . Have you tried to spray carb cleaner or either around your manifold to check for vaccum leaks? Run some injector cleaner through it maybe, maybe a injector is not spraying good. Change your fuel filter. Somethings to look at....

 

[kphilpott1500]

I haven't tried the carb cleaner trick yet but I will. gonna grab a new fuel filter and some injector cleaner today and give that a shot too

 

[GMT604]

Plain water works better, and in some cases you can hear it being sucked into a vacuum leak. And it's not flammable.

 

[Pak713]

How extreme are we talking here? When the idle acts up how much does the rpm gauge fluctuate? If it's extreme I would say there is definitely something going on here. When the truck decides it wants to idle like crap is it when the engine is cold? I would definitely check for vacuum leaks, change the fuel filter and get some good injector cleaner. Like seafoam or chevron techron. Those are the only two I use personally. The idle air control valve could be cleaned as well. They get all gummed up with carbon and will cause a rough idle. If it's not a big difference in the idle but enough for you to notice it, every GM 4.8 or 5.3 truck I've owned has had a fluctuation at idle. Not extreme just a normal GM trait.

 

[kphilpott1500]

Fuel filter and injector cleaner will be happening asap. It's an extremely rough idle! Does it more warm than cold. It's almost a 200-250 rpm surge when it's happening it shakes the whole truck like it has a massive cam and a bad tune lol

 

[country1911]

If its throwing codes for knock sensors, that would be where i would start. They affect timing and fuel trims to prevent detonation. You have to pull the intake to do them. Replacing the intake gaskets at the same time would eliminate a vaccuum leak there as a possibility (common issue).

 

[apcnc]

Could have some water in the fuel. When you change the filter catch some and check. Possibly coil.