My engine has a rough idle why?

Tiny
MTMCALL
  • MEMBER
  • 2003 CHEVROLET SILVERADO
  • 94,000 MILES
Guys, 2003 Silverado 2WD 5.3 w/ 90K.I have been getting codes for MAF, O2 etc. I have replaced plugs, wires, #3 bank, O2 back and cleaned MAF. Still runs horrible. Won't hardly idle when started and will at times die even when to temperature. RPM jumps from 500-900 when in gear. Dealer says gasket on manifold is bad and needs to replace. I can't find a vacuum leak anywhere. I have sprayed starter fluid all around the manifold and can't find anything to indicate what they are telling me. Whay else can cause this. The CEL is still on and my fuel economy is horrible.
Thanks Mike
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Wednesday, January 18th, 2012 AT 5:52 PM

27 Replies

Tiny
BUDDYCRAIGG
  • CERTIFIED MECHANIC
There are two common problems with your truck. The intake manifold leaks coolant into the intake runners or you have a bad fuel injector. These guides can help us see why you have a rough idle.

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

and

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

and

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

Please run down these guides and report back.
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Wednesday, January 18th, 2012 AT 6:17 PM
Tiny
WOODYODA
  • MEMBER
  • 2003 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 204,000 MILES
Rough idle when cold. Runs great when hot. Have replaced engine coolant sensor and maf unit. Got any suggestions? Codes are 171,174, lean fuel mix.
Mike
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Monday, November 16th, 2020 AT 10:55 AM (Merged)
Tiny
RASMATAZ
  • CERTIFIED MECHANIC
Lean fuel condition could be caused by one of the following below:

1. Vacuum leaks
2. EGR and PCV valve.
3. Low fuel pressure.
4. Dirty fuel injectors.
5. Mass Air Flow Sensor.
6. Oxygen Sensor.
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Monday, November 16th, 2020 AT 10:55 AM (Merged)
Tiny
WOODYODA
  • MEMBER
Thanks, my intake gasket was leaking I replace it now the truck runs good again. Great site btw.
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Monday, November 16th, 2020 AT 10:55 AM (Merged)
Tiny
JANSONP
  • MEMBER
  • 2003 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 105,000 MILES
I have noticed the rough idle for awhile and just now noticed when I start it up I puffs black? I have changed the spark plugs, changed the oil and I am going to seafoam it this weekend. It is hard to start sometimes, never in the morning it always fires right up after sitting. When I say rough start I mean, I turn the key over and let go it still tries to crank and wont start so I give it some gas while cranking itand its starts. Like a diesel with the black smoke haha, if you could giveme some ideas to check I would appreciate it, thanks
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Monday, November 16th, 2020 AT 10:56 AM (Merged)
Tiny
LEGITIMATE007
  • CERTIFIED MECHANIC
Hi, I would check a couple of things, one is for a leaking injector or faulty injector, another possibility would be a bad fuel pressure regulator, and a dirty fuel filter.. You must also before doing any of these things, check the fuel pressure and spark. Ill send the links to show you the best way to check
joe
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Monday, November 16th, 2020 AT 10:56 AM (Merged)
Tiny
LEGITIMATE007
  • CERTIFIED MECHANIC
https://www.2carpros.com/how_to/how_to_test_an_ignition_system.htm
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Monday, November 16th, 2020 AT 10:56 AM (Merged)
Tiny
LEGITIMATE007
  • CERTIFIED MECHANIC
https://www.2carpros.com/how_to/how_to_check_fuel_pressure.htm
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Monday, November 16th, 2020 AT 10:56 AM (Merged)
Tiny
MATT M5
  • MEMBER
  • 2003 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 142,000 MILES
Recently I had a battery malfunction on the auxilary battery of my dual battery system. I had to jump the battery to start, after replacing the battery the idle was rough in gear only. I cleaned the fuel system & changed the fuel filter & the spark plugs. I also cleaned all of the cables & terminals of the batteries but still have the problem of rough idle in gear. Batteries are holding their charge. PLEASE HELP!
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Monday, November 16th, 2020 AT 10:56 AM (Merged)
Tiny
FISHERMAN
  • CERTIFIED MECHANIC
Hello !

Vehicles equipped with an engine control module, may require a computer relearn procedure after vehicle battery is disconnected. Vehicle computers memorize and store vehicle operation patterns for optimum driveability and performance. When the vehicle battery is disconnected, this memory is lost, which may result in a driveability problem. Depending on the vehicle and how it is equipped, the following driveability problems may exist:
Rough or unstable idle.
Hesitation or stumble.
Rich or lean running.
Poor fuel mileage.
Harsh or poor transmission/transaxle shift quality.
Default data is used until NEW data from each key start is stored. As the computer restores its memory from each new key start, driveability is restored.
Driveability problems may occur during the computer relearn stage. To accelerate computer relearn process after battery removal and installation, specified computer relearn procedures should be performed. See appropriate procedures for specified manufacturer.

Good Luck!
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Monday, November 16th, 2020 AT 10:56 AM (Merged)
Tiny
FISHERMAN1
  • MEMBER
  • 2002 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 69,000 MILES
Code reader says code 171, 174, system too lean bank 1, system too lean bank 2. How do you fix this problem, and what is the problem.
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Monday, November 16th, 2020 AT 10:57 AM (Merged)
Tiny
JACKSKI
  • MEMBER
I had same codes on my 02 Silverado 5.3, remanufactured MAF sensor cleared codes after a couple cold morning starts. Also cleared cold morning rough idle starts. Autozone told me when both these codes come up together it is most likely the MAF sensor, not the 02 sensors that are bad. Jackski
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Monday, November 16th, 2020 AT 10:57 AM (Merged)
Tiny
JACKSKI
  • MEMBER
Yep, I did all of the fuel injectors runs smooth and has good power.
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Monday, November 16th, 2020 AT 10:57 AM (Merged)
Tiny
AUTODREW
  • MEMBER
  • 2002 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 153,000 MILES
My '02 1500 just started having rough idle issues. The truck starts fine but when its cold out it cant seem to find a steady idle point. Complete tune up done ie. Wires, plugs and filters with fluids.I keep pulling codes for bank 1 and 2 running lean. As soon as the truck warms up or if the outside temp is above 50 it runs great. Please help.
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Monday, November 16th, 2020 AT 10:57 AM (Merged)
Tiny
DENNYP
  • CERTIFIED MECHANIC
You have a vacuum leak at the intake gaskets. You need to replace the intake manifold gaskets. The lean codes are from the unmetered air entering around the gaskets. When the engine heats up, the aluminum cylinder heads expand and seals the leaks.
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Monday, November 16th, 2020 AT 10:57 AM (Merged)
Tiny
GILBERT CASTRO
  • MEMBER
  • 2002 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 113,000 MILES
2002 Chevy silverado 4.8 113000 miles rough idle in cold weather I have replace the fuel filter, fuel regulator, fuel pump and maf sensor (mass airflow sensor). Did not help BUT when I disconnect the maf sensor in the cold morning the idling improves and when reconnect it the idling is rough and wants to stall. When the truck is warm there are no obvious problems until the next morning?
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Monday, November 16th, 2020 AT 10:58 AM (Merged)
Tiny
HIHOSILVER2002
  • MEMBER
My truck does exactly the same as the one listed above. I have just checked a few simple things but have gotten nowhere. Someone suggested that a water temp sensor or an air temp sensor was bad. Is there more than one water temp sensor. The guage reads properly. I would appreciate anyones help Thanks Ron
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Monday, November 16th, 2020 AT 10:58 AM (Merged)
Tiny
RNAEGLE
  • MEMBER
I would also like to see a solution to this problem. I have a 2002 Silverado with only 59K miles and have the same issues?
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Monday, November 16th, 2020 AT 10:58 AM (Merged)
Tiny
MWUNDER
  • MEMBER
  • 2002 CHEVROLET SILVERADO
2002 Chevy Silverado V8 Four Wheel Drive Automatic 138K miles

Hello. I have an '02 Silverado 4WD with 138,000 miles. Last Friday, I took it in for a routine oil change. Saturday morning, the SES light came on and it had a rough idle (more so as it warmed up) and hesitation. Sunday morning, as it was warming up in the garage, I noticed quite a bit of "soot" on the floor from the exhaust. I had the codes read and it came back with P0131, P0300, & P0171. Could all these symptoms be from the o2 sensor, or could something else be triggering that code? Thanks for your help.
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Monday, November 16th, 2020 AT 10:58 AM (Merged)
Tiny
MASTERTECHTIM
  • CERTIFIED MECHANIC
All those problems are from o2 sensor. By you telling me you have soot at tail pipe, means your running real rich. Code 171 means o2 sensor reads lean. By your o2 sensor being bad and always telling computer its lean (171) so it dumps in more fuel to try to make it rich, but no matter how much fuel it gives it, the computer still sees lean. Do you get it. I hope this helps.
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Monday, November 16th, 2020 AT 10:58 AM (Merged)

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