Misfire - rough idle

Tiny
GUTTER
  • MEMBER
  • 2009 CHEVROLET SILVERADO
  • 50,000 MILES
Hi, I have 2009 Chevy Silveraor with about 88,000 kms. Purchased the truck in December and have been having rough idle conditions and what feels to be misfiring(on morning start up, sitting at lights I can feel it, and during the daytime if it has sat for a couple hours). The problems seem to have started as soon as the spring and warmer weather started.

I have had it in to the dealer several times, and here is progression.
1.) At this time the truck if it sat overnight or for a coupel hours when I went to start it up, it would misfire and feel like it was going to stall out. The dealer thought it was bad injectors so they changed two fuel injectors and also told me I should have some sort of fuel injection cleaning process completed as the fuel rail was dirty and they blamed me of either putting bad gas in or that the previous owner (a farmer and dirt roads was to blame). I never did have the fuel injector cleaned or fuel rail clean as I just bought the truck and did not feel I should pay.
2.) The fuel injector replacement did not help anything. So I then took it to a different GM dealer, who confirmed the rough idle after it had sat overnight and also they plotted some sort of graph confirming it was not running correctly. They root caused it to a bad O2 sensor which they replaced.
3.) This seem to help a bit, but not 100%. I went on vacation with the truck and got a code (did not write it down fortunately) saying that the engine was running to lean. When I got back from vacation I took it to the dealer and they said they forgot to hook something up related to the sensor or something else.
4.) It seems when the re-hooked something up the problem of misfiring got worse on startup. So I took it back to the dealer. They told me the only thing they can think of is to replace all 8 of the spark plugs, which I did and paid for. I also asked are you sure this will fix it, of course they said it should.
5.) The spark plugs I changed about a week ago and the truck is still misfiring and running rough, in fact the engine seems to be running worse with the new spark plugs. When I startup the engine it misfires and shakes and I can see the RPM meter fluttering.
6.) I called the dealer to set-up an appointment for them to look at it as something is not right. They told me they are not sure what is going on. They said had no codes when I took it in last time, the only thing they said it might have something to do with carbon build up and I should have some sort of vacuum cleaning system done on it.

So I am not sure what to do right now.I really want to take this truck back and throw the keys at them. Have had to take several days off from work and the headache alone.

Hoping someone can help me out. Is there something else they should be checking and proving to me they did actually check it.

Thanks for the help.

p.S. It is still under powertrain warranty and I bought the extended GM warranty as well.
Tuesday, August 20th, 2013 AT 9:33 AM

31 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,490 POSTS
It sounds like you have an engine coolant temperature sensor that is going out. When these sensors get a little off they wont trigger a check engine light.

Here is a guide to help you see what you are in for when doing the job.

https://www.2carpros.com/articles/coolant-temperature-sensor-cts-replacement

Sometimes as the miles accumulate and a little varnish builds up in them one or two cylinders will start to run a little lean. The extra unburned oxygen in the exhaust is detected by the oxygen sensor as a lean condition, and the Engine Computer reacts by commanding more fuel from all the injectors on that side of the engine, even those that weren't running lean. Your mechanic can find evidence of that with a scanner by viewing the long and short-term fuel trim numbers. They will be very high positive on the side that's running lean.

As for that fuel system cleaning, that DOES seem to be pretty effective in solving a lot of rough running and lean fault codes, particularly on GM vehicles. This is not the simple "mechanic-in-a-can" that you dump in the gas tank. Those chemicals are just concentrated versions of the additives you get in every gallon of gas. The professionals connect their equipment to the fuel rail and disable the vehicle's fuel pump. The engine runs on that highly-concentrated detergent for about 20 minutes.

Please let me know what happens
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Tuesday, August 20th, 2013 AT 10:13 AM
Tiny
GUTTER
  • MEMBER
  • 1 POST
I wish I contacted you first! After all that with the dealer I fixed it myself! Lol thanks for the tip I love this site.
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Wednesday, August 28th, 2013 AT 10:38 AM
Tiny
SMS8577
  • MEMBER
  • 2 POSTS
So was it the coolant temp sensor?
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Thursday, October 4th, 2018 AT 1:24 PM
Tiny
SMS8577
  • MEMBER
  • 2 POSTS
I think this could be my issue, same symptoms same yr model truck, wow
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Thursday, October 4th, 2018 AT 1:39 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,490 POSTS
Yes this was an engine coolant sensor issue. Please let me know what happens. Ken
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Friday, October 5th, 2018 AT 11:48 AM
Tiny
STUMPEDRAUL
  • MEMBER
  • 1 POST
  • 2009 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 144,000 MILES
So originally computer sent out p1400 and p0300. Changed plugs, wires, bought two coils and changed two at a time and no difference. Was loosening fuel PSI when it starts idling rough from 60psi to 44. So changed fuel pump, just changed canister purge valve after a $200.00 diagnosis from a well known shop and also came out a hole in the bladder of brake booster They said. They wanted $1,800.00 to change both parts. I was not paying that for sure. Still rough idle and I am stumped. I am open ears
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Monday, November 16th, 2020 AT 10:37 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,700 POSTS
Hi and thanks for using 2CarPros.com.

First, a vacuum leak will cause a rough idle and it will cause issues with fuel mixtures for the engine. The first thing I would confirm is engine vacuum. If the components which they told you are bad actually are, it will create a vacuum leak. Here are directions for checking for a vacuum leak:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

The P0300 code is a multiple cylinder misfire code. I believe you already know that because you replaced the coils, wires. A vacuum leak could cause that code to show up, so again, confirm there is no leak. The P1400 code is something different but can indicate an vacuum issue. If the intake gasket leaks on cold starts, that is going to change how the computer provides fuel and air to the engine. The system, cold start emission reduction control system, basically causes the engine to idle higher and it retards the ignition timing which in turn, allows the catalytic converter to warm up faster. Now, the technical description of what sets the code is this. The exhaust energy model does not match the expected energy model. Basically, that means the emissions are not what they should be.

Here are some things to check:
1) Make sure there are no vacuum leaks.
2) Confirm that the throttle body is clean.
3) Confirm that the mass air flow (MAF) is clean and not obstructed.
4) If you have a scanner, check to see if the if the coolant temp sensor and the intake air temperature match.
5) If you do have a scanner, this code will save freeze frame data. Basically, your computer can show you what caused the code to set.
6) Make sure the air filter is clean and there are no obstructions.
7) Make sure the PCV is not damaged causing a leak.

Here is a video which shows how to use a scanner, just in case you are unfamiliar with one;

https://youtu.be/YV3TRZwer8k

I hope this helps. Please feel free to let me know if you have other questions. Again, my first suspect would be related to a vacuum leak. Any unmetered air after the mass air flow sensor can set this code and cause a random misfire. Also, my suggestions are based on a vehicle which has not been modified with a different exhaust, cold air intake.

Take care and happy 4th,
Joe
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Monday, November 16th, 2020 AT 10:37 AM (Merged)
Tiny
ALBERTO.ALVAREZ79
  • MEMBER
  • 1 POST
  • 2007 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 91,000 MILES
The vehicle fluctuates while driving at an avg speed of 75mph. Why does it do it.

Replaced the throttle body and the throttle position sensor.
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
I have seen the PCV hose fail because of a broken connector causing this issue here is the location so you can see if that's your problem. Check out the diagrams (Below). Please let us know what happens.
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
JAEDEN
  • MEMBER
  • 4 POSTS
  • 2007 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 169,793 MILES
When parked at idle there is a noticeable light misfire.
When parked in gear there is an aggressive misfire and occasionally when accelerating from a stop it will almost act like it is loading up.

Tested ignition coils, new plugs.
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,490 POSTS
Hello,

These trucks had a big problem with the plug wires. Did you replace those when you did the plugs?

Best, Ken
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
JAEDEN
  • MEMBER
  • 4 POSTS
No I did not, would that make a difference through the rpm range?
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,490 POSTS
O ya big time. It would be good if you can make a video and send me the link so I can see what its doing. It makes it faster to get the problem fixed.

Please let us know what happens.

Cheers, Ken
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
JAEDEN
  • MEMBER
  • 4 POSTS
Alright thanks ken, ill send a video next weekend as I am 3 hours away from it for the week
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Okay

Cheers, Ken
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
JAEDEN
  • MEMBER
  • 4 POSTS
It was a bad fuel injector on #3 cylinder, all set thank you for your help.
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,490 POSTS
Good to hear, please use 2CarPros anytime we are here to help.
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
TAMMYR
  • MEMBER
  • 1 POST
  • 2004 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 153,000 MILES
Changed exhaust system now will not idle good has black liquid coming from exhaust replaced cataliac converters still doing same thing and funny smell when idles
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
How much/what part of the exhaust system did you change? Did you install headers? If so double check the firing order. Has it set a check engine light? If it has a PCM scan may be helpful in figuring this one out
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Monday, November 16th, 2020 AT 10:41 AM (Merged)
Tiny
OCTJAZZ65
  • MEMBER
  • 1 POST
  • 2004 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 76,000 MILES
My 04 Silverado is idleing rough the check engine light is on now. When I drive it, it seems to run fine, only rough at idle at stop lights. Also I live in Nebraska and the weather is cold. When I start it to warm in up in the morning, after a while I will see black soot coming out of the exhaust pipe. How serious of a problem could this be?
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Monday, November 16th, 2020 AT 10:42 AM (Merged)

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