MY HAS A ROUGH IDLE STARTING AT 10 SECONDS AFTER START OF VEHICLE, WHAT IS THE CAUSE?

2002 GMC Yukon

Tiny

Roughidleyukon

November, 2, 2011 AT 1:24 AM

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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21 Answers

Tiny

Jacobandnickolas

November, 2, 2011 AT 1:27 AM

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.

Tiny

Roughidleyukon

November, 2, 2011 AT 1:32 AM

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.

Tiny

Jacobandnickolas

November, 2, 2011 AT 1:34 AM

If the miss followed the coils, then they are most likely the issue. Sorry, I don't know how I missed that.

Tiny

Roughidleyukon

November, 2, 2011 AT 1:38 AM

It did not follow the coils exactly. It was quite random.
Mechanic says spark plugs, wires, coils and injectors were good.

Tiny

Jacobandnickolas

November, 2, 2011 AT 1:40 AM

If it didn't follow them, it could be from a vacuum leak, low fuel pressure, crank sensor or cam sensor.

Tiny

Roughidleyukon

November, 2, 2011 AT 1:44 AM

How do you recommend proceeding from here?
Are these small fixes or quite labor intensive?
And thanks for your help so far.

Tiny

Jacobandnickolas

November, 2, 2011 AT 1:58 AM

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.

Tiny

Roughidleyukon

November, 2, 2011 AT 2:01 AM

Thanks a lot.
I will give a try and let you know what I find out.
Your insight is greatly appreciated.
Thanks again.

Tiny

Roughidleyukon

November, 3, 2011 AT 2:51 AM

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.

Tiny

Jacobandnickolas

November, 3, 2011 AT 2:58 AM

The codes would have been PO302, 304, 306. Did vacuum and fuel pressure check out okay?

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