Rough idle when coming to stop

HondaHawkGT · May 5, 2016

There are likely multiple possible causes for a vibration at idle or rough idle. I think the new K2 engine mounts exacerbate the condition. My bets are on oil ingestion via the PCV system for a lot of guys in this thread with more than 1k miles. The spark plugs or injector orifices are probably sooty from the oil.

New trucks may have a problem with the engine (ignition system, fuel system, vvt system, sensor issue, bad fuel, etc). Search Google for solutions for a rough idle... the possibilities are endless. It's also a common issue on virtually every make and model.

The few times I had a rough idle, I fixed it with intake cleaner. I've kept it away with a catch can and good fuel (89+). I've had my AFM system disabled since the first 1k miles or so. My engine always seemed to run a bit rougher after extended highway trips with AFM active.

schnezz · May 5, 2016

With having less than 1,000 miles on my 16 slt I have the same issue. Since I picked it up with only 10 miles on the truck, I figured it was just the cheap gas the dealer had it filled with at delivery. I've ran nothing but high test through break in and gave GM the benefit that it would go away. Needless to say it has not. I have no problem taking it to the dealership when I get a free day but would like a little fire power when I get there. My thought of the service writer saying that's what try do and no fix is unacceptable

HondaHawkGT · May 5, 2016

Yeah no matter what manufacturer made the vehicle, they'll almost always say it's "normal". They ought to at least do a few physical checks, not just scanning the computer. Pull and inspect the spark plugs, spark plug wires and coils, etc.

twoheeldrive · May 9, 2016

Add me to the list of shaky idle. It's intermittent though, usually after I stop after exiting the highway and sitting on the exit ramp waiting for the light to change. Idle is just a little under 500RPM and steady. If I shift to neutral it goes away until I put it back in drive.

A little bit annoying, to be sure and its done it since day one. It now has 5000 miles, I run premium fuel and have had a catch can for the last 4500 miles. It did it on regular fuel too. I figured it was one of those, "they all do that" things. I might take it in, but am afraid they will blame the catch can.

Linecapt · May 11, 2016

There apparently must be some problem with the 5.3's, as either they aren't supposed to drop to fuel management mode when at idle or there is something they can't fix or don't want to. In March I turned in my leased '13 Silverado with the 5.3. The same day I took delivery in 2013 I brought it back saying there was a problem with the rough idle. I asked them to find me another on the lot to compare it to, and it did it too. Just another thing I didn't like about the truck, hence why I didn't keep it. Suppose you have to live with it or have the idle bumped up, if you can. After a while, you won't notice it any longer as it'll be routine.

2015Z71 · May 12, 2016

My dealer wants to do the shim fix on my truck. Has anyone seen success with this.

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mookdoc6 · May 14, 2016

Chalk me up with the problem! No way it's washers to fix this.........Mine is fine driving and in gear the minute I put it into Park only with the AC on does it get harsh and lumpy with the tach moving 300-600 and around?

mookdoc6 · May 14, 2016

I am getting splash guards put on tomorrow morning so I will ask.......Why bother I will be told there is nothing wrong with. And by the way one of our 15yr old retarded workers F Up'd your splash gaurds sorry bro! I just know it's going to be some shitty job done on it!

everclear86 · May 14, 2016

I'm having a similar issue. On startup the engine runs smooth and normal but yesterday leaving from work I accelerated from a stop sign and heard a clunk and then the truck had a vibration to it and seemed like it had no power. The clunking happened a few times on the way in to work today as well. Coming up to a stoplight, the truck shakes pretty bad and has a growl to it. Never has done this before and I have 50k on it. Even at freeway speeds it the exhaust sounds deeper and i have to work the pedal to get it to down shift to speed up whereas before ot was smooth. I will check MAS tonight along with tire pressure. I have no idea what it is but I'm wondering if it's the torque converter. Any ideas?

ridethedesert · May 15, 2016

2014 GMC Sierra 5.3, every once in a while I get a rough idle at a traffic light. I've found the cause to be a dirty throttle body. Remove the air intake, spray throttle body cleaner and clean it with a new rag. Clean the plate and the sides of the body. Reassemble. Rough idle gone. Happens about every 15,000 miles to me but could be sooner depending on what gas you use. Cheaper gas it could happen within 500 miles, especially here in California with our special crap blend. You should see what it does to dirt bike carburetors. I'm running Shell 91 octane. On my 2004 GMC this was a dealer recommended service every 15,000 miles.

ridethedesert · May 15, 2016

* Deposits that form in the throttle body can reduce airflow through the idle bypass circuit affecting idle quality and smoothness. These deposits are formed by fuel vapors that rise up through the intake manifold.

HondaHawkGT · May 17, 2016

* Deposits that form in the throttle body can reduce airflow through the idle bypass circuit affecting idle quality and smoothness. These deposits are formed by fuel vapors that rise up through the intake manifold.

The 2014+ trucks don't have an idle air control circuit that older trucks had. It used to be controlled by an "IAC valve" that would act up and cause idle issues. The other airflow circuit is the PCV system. The newer PCV system design dumps vapors directly inside the intake manifold, bypassing the throttle body. I'm willing to bet some 2014+ trucks have a rough idle due to oil & combustion vapors pulled in from the PCV system. My catch can has plenty of oil in it everytime I check it (1oz per 1k miles). That much oil could foul a spark plug or deposit on the intake valves, creating issues.

Cvincent · May 19, 2016

I have the same problem, dealership said that it is active fuel management and the fact that the timing is retarded to the extreme to help the truck get optimal fuel mileage.... that's what they said. "its normal"

20L8TSierra24 · May 20, 2016

I've had a rough idle, even after tuning to idle at 600RPM. Last night I Seamfoam'd the intake and no more rough idle! Smooth as butter

And now you'll get a CEL for the cats being clogged. My brother sea foamed his and the cats were throwing codes 2 k later. Needless to say he has new cats now

Alter · May 20, 2016

Our new 2016 Silverado(500km) has a somewhat rough idle also when parked. I notice the tach shimmy and it feels like the truck has a miss or too low of a idle. I'll be bring this up when I go for my first oil change to see what they have to say. Maybe like with our Canyon I had to tell them what needed to be fixed after their recall screwed up the steering system.

Something else I noticed is when you start up the air conditioning there is IMO a old PCV valve oil smell comes out, my wife says its still new but I remember that smell from the olden days. We have only had the truck for a week now and sure hope it goes away.