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My 2002 Yukon has a rough idle starting at 10 seconds after start of vehicle, what is the cause?

Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 2002 GMC YUKON
  • 111,000 MILES
I have changed spark plugs and wires myself.
I took Yukon to mechanic and he confirmed my work good.
He tested and it would give a misfire on a certain cylinder than he would reset and do again and it would give a different cylinder as a misfire. He did compression tests and all checked out. He removed the fuel injectors and tested and all were good. He took coils from the side of engine giving misfires and swapped with other side but problem persisted.
Truck runs fine at higher rpm. Only runs rough (misfire) at idle
Any help would be appreciated.
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Wednesday, November 2nd, 2011 AT 1:24 AM

21 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
If the problem stayed in the same cylinders, try switching the fuel injectors to see if that changes anything. If it doesn't check compression in the affected cylinders.
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Wednesday, November 2nd, 2011 AT 1:27 AM
Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 11 POSTS
It did not stay in the same cylinders all the time.
Fuel injectors were tested and checked out OK.
Compression test was done as well and checked out OK.
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Wednesday, November 2nd, 2011 AT 1:32 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
If the miss followed the coils, then they are most likely the issue. Sorry, I don't know how I missed that.
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Wednesday, November 2nd, 2011 AT 1:34 AM
Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 11 POSTS
It did not follow the coils exactly. It was quite random.
Mechanic says spark plugs, wires, coils and injectors were good.
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Wednesday, November 2nd, 2011 AT 1:38 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
If it didn't follow them, it could be from a vacuum leak, low fuel pressure, crank sensor or cam sensor.
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Wednesday, November 2nd, 2011 AT 1:40 AM
Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 11 POSTS
How do you recommend proceeding from here?
Are these small fixes or quite labor intensive?
And thanks for your help so far.
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Wednesday, November 2nd, 2011 AT 1:44 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
On our homepage, there is a diy for the vacuum test. As far as the crank sensor, it will require special tools and some labor. Just a thought, make sure the spark you get to the plugs is a hot blue spark. Also, on the homepage under diy are the directions for checking fuel pump pressure. There is also a video to help.
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Wednesday, November 2nd, 2011 AT 1:58 AM
Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 11 POSTS
Thanks a lot.
I will give a try and let you know what I find out.
Your insight is greatly appreciated.
Thanks again.
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Wednesday, November 2nd, 2011 AT 2:01 AM
Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 11 POSTS
I spoke to the mechanic today and he did the vacuum test, fuel pressure test and he said he didn't get any codes that would have indicated crank or cam sensors.
The code, I think, he gets is 302? - Misfire on 2, 4 or 6.
It may show misfire on 2, then he would do over and it would then show on 4 or 6. Very random and inconsistent between these three cylinders.
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Thursday, November 3rd, 2011 AT 2:51 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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The codes would have been PO302, 304, 306. Did vacuum and fuel pressure check out okay?
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Thursday, November 3rd, 2011 AT 2:58 AM
Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 11 POSTS
Yes, PO302.
Vacuum and fuel pressure check out good.
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Thursday, November 3rd, 2011 AT 3:02 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
It has to be electrical then. The crank, cam, or other sensor that is breaking down. It could also deal with the computer itself.
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Thursday, November 3rd, 2011 AT 3:05 AM
Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 11 POSTS
Mechanic mentioned asking dealer if there are any ECM updates.
Next he said the actual cam shaft may be wearing. What is likelihood of cam shaft wearing?
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Thursday, November 3rd, 2011 AT 3:09 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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The computer could need flashed. That is possible. As far as the cam, they had problems years ago with the 350CI. However, if you kept your oil changed, 111K is nothing on this engine.
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Thursday, November 3rd, 2011 AT 3:12 AM
Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 11 POSTS
I'll call dealer tomorrow and ask if they have any updates.
I thought the same about the miles.
Anything else I should ask regarding the computer?
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Thursday, November 3rd, 2011 AT 3:17 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
Explaine what it is doing. It may prompt them to remember an update.
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Thursday, November 3rd, 2011 AT 3:33 AM
Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 11 POSTS
Thx again.
Will keep you posted.
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Thursday, November 3rd, 2011 AT 3:35 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
Glad to help. It would be easier if I was there. Just an FYI. When you get a PO300 code, that is a random misfire. From there, the computer will indicate specific cylinders that are missing by the last number. For example, PO301 means the number 1 cylinder is missing. A PO304 would mean cylinder 4 is missing and so on. Just a little info to help you understand.
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Thursday, November 3rd, 2011 AT 4:01 AM
Tiny
SEVEREDHEADS
  • MEMBER
  • 2 POSTS
If all your misfires are on the right bank, try removing right upstream O2 sensor. The one between exhaust manifold and catalytic converter. If the misfires go away or are less frequent, you have an exhaust restriction. Probably the cat.
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Thursday, November 3rd, 2011 AT 5:12 AM
Tiny
ROUGHIDLEYUKON
  • MEMBER
  • 11 POSTS
If it was an exhaust issue, would my check engine light come on because it has not come on as of yet.
It's been idling rough for approx. 1 month now.
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Thursday, November 3rd, 2011 AT 7:46 PM

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