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Rough Idle - Codes P0151, P0174, P0300

Tiny
DWILSON39
  • MEMBER
  • 2005 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 66,650 MILES
Tahoe is running very rough at idle, almost stalling. Check Engine light is on, Onstar Diagnostic says to have car serviced, emissions control error. Actuall codes are P0151, P0174, P0300. Replaced plugs (AC Delco), Wires, and new Interstate battery. Added fuel injector cleaner. Only 66650 miles, passenger side plugs were all fouled, driver side normal deposits. Still running rough with "rotten egg" smell from tailpipe at idle. Runs fine at speeds above 20 mph.

Any suggestions before I bring to dealer? Warranty is no longer valid, but have a engine and transmission warrantly thru original dealer in CO, vehicle in WY.
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Monday, January 5th, 2009 AT 11:36 AM

58 Replies

Tiny
BRIAN 1
  • MECHANIC
  • 1,030 POSTS
Hello,

This occurs when the engine misfires causing the oxygen sensor codes lets start with a compression test to see if the engine is okay before we go any further, here is a guide to help.

https://www.2carpros.com/articles/how-to-test-engine-compression

Please run down this guide and report back.
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Monday, January 5th, 2009 AT 3:34 PM
Tiny
ARTENEZ3
  • MEMBER
  • 1 POST
Thanks for this post I had this problem and used the guide found the #3 cylinder had 30 psi time for a valve job. I love this site.
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Sunday, July 28th, 2019 AT 6:03 PM
Tiny
DERREK DEITRICK
  • MEMBER
  • 1 POST
  • 2004 CHEVROLET TAHOE
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 165,000 MILES
Started with a squealing belt now I am having problems idling.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Belt and tensioner should be replaced at 60,000 miles due to losing tension and wear. Do not a spray any soap or oil on the belt it will destroy it. Then clean throttle plate on both sides and IAC hole with choke cleaner. If stalling continues check fuel pressure with a gauge auto parts rent it.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
MASYGA
  • MEMBER
  • 1 POST
  • 2004 CHEVROLET TAHOE
  • V8
  • AWD
  • AUTOMATIC
  • 73,000 MILES
I have an 04 tahoe that was getting the SES error code of p0174. Currently the light is off but the car is running rough at idel and it gets worse as the out side temp gets colder.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (Try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
NAVYTECH79
  • MEMBER
  • 7 POSTS
  • 2000 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 110,000 MILES
I have a 2000 Tahoe and a few months ago noticed that the engine was idling very rough and used the gas supplements a few times and the problem went away. Now it seems the problem is back and worse. I have tried the supplements, but no joy. Took the vehicle in to have the injectors cleaned and it seemed ok for a few days. But the problem is back. Since then I have noticed that while driving @ 45-50 mph the engine looses power and stutters. If I let off of the accelerator it stops stuttering. If I try to accelerate through and above 50 mph it has a hard time doing so. Please help me out. Thanks.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
Is the check engine light on?
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
NAVYTECH79
  • MEMBER
  • 7 POSTS
No, that would have helped. The guys at the auto part store said that it would be very costly to take it in because the check engine light is not on. Sorry, this doesn't help.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
Ok, that usually means that all the sensors etc. Etc. That are regulated by the computer are reading within spec.
There is a common problem with the fuel injection system on these engines. GM is VERY aware of this and has developed an upgraded fuel injector system for this problem. The problem is that a GM dealer must determine that this problem exists. The fact that you had the injectors cleaned and you had briefly positive results, leads me to believe that it is a fuel problem. A failing fuel pressure regulator is common and this may be your problem. However, this part is located under the upper intake manifold cover. Your injectors are also located and accessed under this cover. This cover should not be taken on and off a lot -- SO -- if you can get the chevy dealer to determine that the fuel injector system is to blame, they should repair this for free. And if a new upgraded injector system is installed they all come with a new fuel pressure regulator. Whoa!
OR LOL
Check your spark plugs. If you replace them or anyother ignition related item, make sure you use A/C Delco parts -- just trust me. If the gaps are good -- what do they look like? And be specific as to what cylinder they came out of.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
NAVYTECH79
  • MEMBER
  • 7 POSTS
I took it into a mechanic and her noticed a strange hissing noise coming from the PCV valve and took it out and said I should replace that and let him know how it runs. I did and it seems to be running good, other than every once in a while it still idles rough.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
Check the fuel pressure.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
JAYIGN
  • MEMBER
  • 2 POSTS
  • 2002 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 100,000 MILES
I have a 2002 Chev Tahoe and last winter/spring when the air temp was between 10-30 F the idle was rough then when the air temp warmed up for summer the rough idle went away and it idled great all summer, now that the air temps are falling the rough idle came back. This is odvusly a temptrature sensor failure of some sort. Do you have any sugestions of where to start (oxigen sensor? MAP Sensor? Fuel pressure regulater?)
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
NAVYTECH79
  • MEMBER
  • 7 POSTS
Sorry, I didn't mention it. That was one of the things the mechanic checked also and said it was good.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
JAYIGN
  • MEMBER
  • 2 POSTS
I forgot to ask about the Idle Control Valve. Could this cause this rough idle. The rough idle is a rich fuel mixture.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
Put some tectron fuel injector cleaner in the gas tank. Cheveron makes it. This may help. But as I mentioned before, check the spark plugs and wires, and make sure the injectors are pulsing (firing) properly. Did the mechanic check the fuel pressure regulator? This is a common failure.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
On left front cylinder head fine engine coolant temp sensor if faulty will not signal PCM engine cold to rich fuel mix so rough idle.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
NAVYTECH79
  • MEMBER
  • 7 POSTS
I don't think he checked the fuel pressure regulator, but the spark plugs and wires are new. Just replaced them Yesterday.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
PEAR69
  • MECHANIC
  • 1,482 POSTS
What brand wires and plugs did you use?
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)
Tiny
NAVYTECH79
  • MEMBER
  • 7 POSTS
I know that the plugs are AC Delco. They did not have AC Delco wires, so I told the guy at the auto parts store to give me the wires one step above them then.
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Sunday, July 28th, 2019 AT 6:04 PM (Merged)

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