Rough idling 2005 Chevy Silverado

maproy99 · Jul 19, 2012

I keep having a rough idling issue on my Silverado (5.3 liter v8 flex fuel) after high RPM for a short time. Happened 5 times within the last 30 days, 2 of which where while I was towing the boat the the others were when I was running late and flooring it. Sometimes the engine miss fire warning light came on, other times I could feel it. It corrected itself if I restarted the engine. Before this I had the downstream O2 sensor code come up, but this was due to "crap" build up on the airflow sensors and/or throttle. Any ideas on what this could be?

fat fanny · Jul 19, 2012

Re: Rough idling 2005 Chevy Silverado

Try checking your fuel pressure possilby low due to failing fuel pump, also could be carbon build up on the idle control valve. There a few other checks I can't think of at this time (a little early) Good luck!

hrdwrkingacguy · Jul 19, 2012

Re: Rough idling 2005 Chevy Silverado

Do you have a cold air intake or is it factory? My CaI makes my mass air flow sensor dirty and the throttle body...I cleaned both of those and idled a lot better...On my truck the amount of air it sees at the particular throttle position is wrong because of the CaI and it will put it in limp mode or something when it for long enough like that...It always throws a 0101 or a O2 sensor code...

dolluper · Jul 19, 2012

Re: Rough idling 2005 Chevy Silverado

Idle air control...dirty ,leaking on TB or secondary air check valve D/S rear of engine,hoses leaking,EGR carboned up,ignition coil wires or ground,spark plugs

maproy99 · Jul 19, 2012

Re: Rough idling 2005 Chevy Silverado

I'll start with the easiest first. Truck only has about 66,000 miles on it.

HopinImFloatin · Jul 19, 2012

Re: Rough idling 2005 Chevy Silverado

start by cleaning the throttle plate and throttle bore, this engine is drive by wire and doesnt use idle air control valve, this is done with the throttle body. this is the easiest and fastest thing to do and its free! If this doesnt help and the misfire is
ONLY at idle, it may be a sticking valve due to carbon. seen alot of this lately. if its a secondary electrical misfire(plugs, wires, coil), it will misfire worse under high electrical load such as pulling a hill in OD with tcc locked up at about 45mph, just before it shifts out of tcc and into a lower gear. this is a good place to start, really hard to say without a scanner to see whats going on.

lncoop · Jul 19, 2012

Re: Rough idling 2005 Chevy Silverado

I used to have a 2005 Sierra (not flex fuel) that did the same thing. Ended up replacing the cats under warranty.

dolluper · Jul 19, 2012

Re: Rough idling 2005 Chevy Silverado

. "Sometimes the engine miss fire warning light came on'OP qote.......usually a spark ,ignition issue when that happens ......coil,coil wires or green ground at coil or bad spark plugs

maproy99 · Jul 20, 2012

Re: Rough idling 2005 Chevy Silverado

Well, it happened to me again this evening. I was rushing into town and got the misfire light coming on a lot. Didn't have an issue with going 0-60mph range but more like the 30-50mph range. And I have another O2 downstream sensor code to clear again. My neighbor will be back Saturday morning and I can use his scanner to clear the code and not get any better idea about what is happening. All it said before that there had been a misfire condition detected, which the light tells me.

dolluper · Jul 21, 2012

Re: Rough idling 2005 Chevy Silverado

What code did you get PO300 is radom misfire.....now you have 8 cylinders so if PO301 its # one cylinder up to PO308 which is # 8 cylinder......so if you got PO305 thats # 5 cylinder see how it works.....you could also have a bad fuel injector or two,three

maproy99 · Jul 22, 2012

Re: Rough idling 2005 Chevy Silverado

My neighbor left again for the weekend, but he'll be back tomorrow night. I lost the codes from the first time we checked, he wrote them down. So, codes will come in then. But, in the meantime, I'm going to clean the mass airflow sensors and see what that does. And when I'm not working on that, yard work, UGH!!!

maproy99 · Jul 22, 2012

Re: Rough idling 2005 Chevy Silverado

Ok, code P0131 and code P0300

dockwrecker · Jul 23, 2012

Re: Rough idling 2005 Chevy Silverado

Mine did the exact same thing about a year and a half ago at 74000 miles. Warped intake manifold! They're plastic. It would throw out the O2 code and a lean fire condition code. My local shop sees about 20 per year. Very common in the 5.3's apparently. New intake gaskets wont fix it, the manifold visibly warps about .040 at the ports. The new replacement intake manifolds supposedly won't warp as easily as the originals. Set me back about $800 to have it replaced.

maproy99 · Jul 23, 2012

Re: Rough idling 2005 Chevy Silverado

Well, I only have a little over 65,000 miles. I'm hoping that cleaning the airflow sensors will fix it. Haven't gone for a drive yet.

dockwrecker · Jul 23, 2012

Re: Rough idling 2005 Chevy Silverado

I started there too. Helped slightly for a day. Came right back. Money says it's the manifold.

MWG2600 · Jul 24, 2012

Re: Rough idling 2005 Chevy Silverado

I have been working on the ls motors for years now, never herd of a warped manifold. i would place my bet on bad catalytic converts!

bkopp85 · Jul 24, 2012

Re: Rough idling 2005 Chevy Silverado

I used to work at a gm dealership. We used to see the warped manifolds all the time. GM used to sell a thicker gasket kit to help. It rarely worked so they i think they only offer the "better" manifold now.

lncoop · Jul 25, 2012

Re: Rough idling 2005 Chevy Silverado

MWG2600 said:
I have been working on the ls motors for years now, never herd of a warped manifold. i would place my bet on bad catalytic converts!

Seems like I heard someone else mention that too.

My '05 Sierra was nothing but trouble. The dealership I bought it from took great care of me as long as I had it, including replacing the cats under warranty even though the warranty had expired. After they did that I threw in the towel and bought an Expedition. Four months later I had to drop six bills on a new throttle body LOL.:facepalm: Seems it doesn't matter what you drive any more. They all have their endemic issues.

maproy99 · Jul 26, 2012

Re: Rough idling 2005 Chevy Silverado

dockwrecker said:
Mine did the exact same thing about a year and a half ago at 74000 miles. Warped intake manifold! They're plastic. It would throw out the O2 code and a lean fire condition code. My local shop sees about 20 per year. Very common in the 5.3's apparently. New intake gaskets wont fix it, the manifold visibly warps about .040 at the ports. The new replacement intake manifolds supposedly won't warp as easily as the originals. Set me back about $800 to have it replaced.

Well, I did a test using the setting to check misfires. Even cylinders have 0 or 1 misfires in their history. Odd cylinders have about a 2,000-3,000 misfire average. That was from me driving roughly 20 minutes into town. When my misfire light came on, cylinder #5 jumped up about 5,000 times of miss firing. This makes me assume that it is a problem on one side of the engine.

dockwrecker · Jul 27, 2012

Re: Rough idling 2005 Chevy Silverado

maproy99 said:
Well, I did a test using the setting to check misfires. Even cylinders have 0 or 1 misfires in their history. Odd cylinders have about a 2,000-3,000 misfire average. That was from me driving roughly 20 minutes into town. When my misfire light came on, cylinder #5 jumped up about 5,000 times of miss firing. This makes me assume that it is a problem on one side of the engine.

Try this. Spray carb cleaner on the odd side intake manifold/head while it's running. If it revs or stumbles, that's where your leak is!

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