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Discussion Starter · #1 ·
I have a 2000 Silverado 5.3L automatic 4x4 w/ dual exhaust.

I've only ever owned Chevy trucks (2005 silverado Z71, 2001 2500hd 8.1L, 2002 Blazer) so I know this is not "normal" chevy roughness.

When I am at a stop light, there is a definite roughness to the idle. It is intermittent and not constant. It is noticeable to passengers, and you can see a vibration of the engine when the hood is popped. There is no pattern to the roughness. It feels like "shake, shake, smooth, shake, smooth, smooth, shake, shake, shake, etc) It seems to be worse in colder weather. Some days in the summer this roughness feels almost non existent. If it was a consistent roughness I can live with it. The randomness of it is driving me nuts.

The idle needle DOES NOT move. But you can definitely feel a change in the smoothness of the idle.

There is NO SES light and NO codes.

If I apply a bit of gas in neutral and bring the RPM to 1000, the roughness is still present but is less pronounced. Above 1000 RPM you cannot feel it anymore. When driving, there is no issue at all and the truck is running great.

I've searched all the forums and have done the following, but it has not helped one bit:
-New AC Delco plugs
-New Wires
-Cleaned MAF
-Cleaned Throttle Body
-Cleaned IAC valve
-Seafoam in gas tank

Next steps:
-Intake Manifold Gasket replacement
-Injector removal and taken to shop for testing/rebuild

Is there anything else I'm missing?

Is there any tips/pointers for identifying the cause of this?

Help me keep my truck ownership pure Chevy, because I'm beginning to have second thoughts...

Thanks
 

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Sounds like either a vacuum leak or a bad sensor. Since you have cleaned alot of sensors you could try running it and misting starter fluid over the air tubes and see if you get a revving.

And did you Gap the plugs according to that years specs? That can also cause a rough idle even after replacement.
 

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Discussion Starter · #3 ·
Thanks for the response.

The plugs were replaced with AC Delco 41-962 which are pre gapped to the. .40 spec. Of note, There is a slight noticeable increase in throttle response since the plugs/wires were changed, so that's good. There has been no change in the rough idle.

For vacuum leaks - shouldnt they cause an actual idle fluctuation? Shouldnt my idle show constantly higher on the tac, or maybe even an idle fluctuation?

My idle is a constant ~500rpm at idle in drive, yet there is a rough intermittent vibration coming from the engine.

Could this have something to do with the harmonic balancer? Or would a balancer issue only get worse as rpms increased?

When my rpms increase the issue (or at least the ability to feel it) goes away and the truck is smooth as silk.

Oh yeah, I had guys from work hop in and they felt it too - so I'm not nuts.
 

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Im having the same issue on mine. Like you, gsauer, Im a Chevy addict. Im 90% sure mine is being caused by a vacuum leak. I hear an intermittent high whistle on the drivers side. and theres rough starts ONLY when the temp is cold. I replaced all my outer vacuum llines to no avail- pre purge and post purge. Next is either the intake gasket or valve cover gasket. If anything, im thinking its the valve cover, as it was replaced in June, when I took it in for the AFM updated cover/ oil pressure regualtor. While spraying it did cough slightly, but not when I sprayed my lines. It was on a slip. Im going to use a fog machine to flush out the issue. ($30 over a $90 test or $1500 for smoke machine).
 

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Chevys do have a common problem with the intakes leaking especially when it gets colder out, but normally when they start going its very noticable and you will get ses lights and everything. Only other thing you can try that i can think of that some people swear by at my dealer is the BG additive 109 that you put in before changing your oil and get it nice and hot. Its supposed to help stop that rough idle
 

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gsauer80 said:
I have a 2000 Silverado 5.3L automatic 4x4 w/ dual exhaust.

I've only ever owned Chevy trucks (2005 silverado Z71, 2001 2500hd 8.1L, 2002 Blazer) so I know this is not "normal" chevy roughness.

When I am at a stop light, there is a definite roughness to the idle. It is intermittent and not constant. It is noticeable to passengers, and you can see a vibration of the engine when the hood is popped. There is no pattern to the roughness. It feels like "shake, shake, smooth, shake, smooth, smooth, shake, shake, shake, etc) It seems to be worse in colder weather. Some days in the summer this roughness feels almost non existent. If it was a consistent roughness I can live with it. The randomness of it is driving me nuts.

The idle needle DOES NOT move. But you can definitely feel a change in the smoothness of the idle.

There is NO SES light and NO codes.

If I apply a bit of gas in neutral and bring the RPM to 1000, the roughness is still present but is less pronounced. Above 1000 RPM you cannot feel it anymore. When driving, there is no issue at all and the truck is running great.

I've searched all the forums and have done the following, but it has not helped one bit:
-New AC Delco plugs
-New Wires
-Cleaned MAF
-Cleaned Throttle Body
-Cleaned IAC valve
-Seafoam in gas tank

Next steps:
-Intake Manifold Gasket replacement
-Injector removal and taken to shop for testing/rebuild

Is there anything else I'm missing?

Is there any tips/pointers for identifying the cause of this?

Help me keep my truck ownership pure Chevy, because I'm beginning to have second thoughts...

Thanks
Try replacing your spark plugs?

You might want to do that.. or at least check the current spark plug gap settings that your current plugs are set at.

Or it could even be your 'M.A.F. Sensor' (Mass Air Flow Sensor) which can cause rough idling/running.

Might even be your fuel pump going out..?? Clogged fuel filter.. or really dirty fuel injectors.

Or, could be a combination of all of those things.

Best of luck though.

By bet would be either the spark plugs needing replaced and set at the proper gap setting.
 

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if you replaced your plugs and have the exact same symptoms then its not the plugs. Does the 00 5.3 have a distributor cap. I can't seem to figure out which trucks stopped using a distributor.
 

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Discussion Starter · #10 ·
Thanks all for the tips. Ive already done the plugs and the 5.3l does not have a cap. GM went to coil packs in 1999 when they released the 5.3l.

I checked my injectors by doing the long screwdriver trick. All are at least engaging as they should be. Still no way for me to check spray pattern/volume, but Im less inclined now to remove the injectors and take them in at $20 a pop.

I also tested for vacuum leaks at the intake manifold with some throttle body cleaner, but no dice.

So Im kind of at a standstill since my 2 hunches dont seem all that likely. I will still go forward with an intake manifold gasket replacement this weekend and hope for the best.

Again Im just shocked that if this is a vacuum or fuel issue, why does the idle not fluctuate? Its almost like the engine is unbalanced or something.

I will report back after the gasket.
 

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Before you do anything else I would change the fuel filter, it is cheap and easy to do. If the problem still persists check your fuel pressure. Without a CEL it is difficult, because currently you do not know if you have an issue with a single cylinder, or if you are getting a random cylinder mis-fire (which I have experienced and can be very difficult to diagnose). If you have confirmed it is not a vacuum leak, and you still cant read any codes to better pinpoint what is causing the problem, the only choice is to start throwing more parts at it. Start with the easiest and cheapest, MAP sensor, IAC, TPS, Injectors, coil packs, etc. Also with the sensors you can often just swap them, run the truck and if the problem is the same swap them back and return it. Good luck!
 

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if you replace the intake gaskets, do the knock sensors while your inthere along with the knock sensor harness.. (may not be cheap depending on where you are), but its good insurance (and use GM products)

have you checked cylinder compression? coolant level; oil level? maybe a bad head gasket or head?
 
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