2000 Sierra 5.3L rough idle - no codes

[70GTORAG]

Been noticing this for a while and have just ignored it until now. At operating temperature during idle the engine typically runs at 500-550 and has a slight vibration to it as if there is a small misfire. You can see the engine has an occasional stutter/shake to it causing the the constant slight vibration. You can also feel it sitting in the truck. Keep in mind it is very slight and the check engine light has never appeared. I do not think it is normal but others might. What makes me think that it is abnormal is the gas mileage on this truck is 13.5mpg, and I think there is something causing an incomplete combustion. Never had it in a shop and dont plan to, but will list the maintenace performed recently. Truck has 130,000km on it.
1. GM plugs 1 year ago.
2. New MSD wires.
3. Cleaned Throttle Body, MAF sensor, and IAC sensor.
4. Inspected EGR-looks clean no blockage. Voltage varies from .86 - 4.69 when pintle is moved through full range(harness connected).
5. New PCV valve.

I have inspected the vacuum lines but have not tested intake gasket or throttle body gasket as I am leary of spraying carb cleaner all over the place to see if the engine idles up. I would also think that if it is a gasket leak the 'rough idle' would be more severe. I think that I have sufficient spark although know nothing about coil packs? This leads me to believe that it lies within fuel management. Anybody else out there annoyed by slight idle problems or can anybody steer me in the right direction? What are the steps for a proper diagnosis?

[maxwedge]

This can be a tough diagnosis, yes a slight vacuum leak can cause this, this would show in the fuel trims, also dirty injectors are a possibility, a dedicated injector clean may be in order here. Do a full scan and look at all the sensor inputs see if you see something astray. A not so definitive roughness is always tough, as I said.

[70GTORAG]

I am going to try the intake and throttle body for leaks as curiosity will get the best of me and I also want to rule them out before moving on. I have also thought about dirty injectors but have done nothing to this point, what do you mean by a 'dedicated injector clean'? I am assuming an additive to the fuel tank from the local parts store, or does GM have an injector clean, if so what brand is recommended?

[maxwedge]

An injector cleaning process that is run thru the pressure port for the fuel pump, the pump is disabled and a pressured can and adapter are connected to the port and the engine is runs off the solution in the can.

[SherylUpchurch]

Hi, Just a quick note on your post. My Husband's 1995 GMC Sierra K1500 was doing the same thing. Rough idle, step on the gas and it was kick and hesitate, it did this for a good 2 1/2 to 3 years. Just the other day I read a post on the JEEP forum (cause I have a jeep) and noticed that someone was having a problem with that too. They put some Marvel Mystery Oil in the gas tank and in the oil crankcase and it worked. Well I will tell you I swear by that stuff....my husband put about 3-4 ounces in the gas tank last time he put gas in and the thing is as smooth as a babies butt!!!! My husband is thrilled he can drive now and not have it idle rough and not have it kick and buck on acceleration....Hope that it helps you too!!!

[kdub55]

I also have a 2000 Sierra 5.3L and min will do that from time to time while i'm sittin in park.Every now and then it'll jump when I hit the gas after it has been vibrating. But it'll usually quit after I get to goin.I guess if it's bad enough, let a mechanic take a look. Good Luck