Rough idle, performance

Tiny
JAMESLEPPEK
  • MEMBER
  • 2007 GMC SIERRA
  • 49,000 MILES
I have a 07 gmc with the 5.3 liter engine. I have reciently been having idle problems and not running right, mostly when first starting and driving the vehicle. After 5 or so minutes it sems to run ok, but still doesn't idle when coming to a stop. I have replaced the spark plugs, washed and re-oiled the filter, and have the oil changed religously every 3000 miles. What next?
Saturday, September 22nd, 2012 AT 5:29 PM

3 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Have the idle control system checked. Cleaning the throttle body and IAC should help.
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Saturday, September 22nd, 2012 AT 6:35 PM
Tiny
JAMESLEPPEK
  • MEMBER
  • 2 POSTS
I have cleaned the throttle body with CRC throttle body and air intake cleaner. It did have some carbon on the throttle body and the "flap" don't know quite sure the name of it. But I cleaned it by using a lint free cloth by hand with the use of the cleaner and it looked great when I was done, the problem I'm having now is that it wants to take the idle up over 1000 rpm and doesn't want to come down to 600 rpm for at least 10-15 seconds. Why did this happen when all I did was clean the throttle body and flap and didn't do anything else? Very puzzled.
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Saturday, September 29th, 2012 AT 11:29 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
The engine computer is programmed to increase the idling speed during cold start till it receives signals from the various sensors that it is ok to reduce the idling speed. When the idle air passage air flow has any restriction due to accumulation of dirt, it would affect the idling, which in your case was improper idling at cold start.

Cleaning of the throttle body has restored the air flow and the difference is what we should be expecting, meaning you have resolved the problem.

That is the reason we suggested cleaning the throttle body and a good thing is you asked after performing the job. It is much easier for us to explain rather than you asking when you don't understand or know what could happen.
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Sunday, September 30th, 2012 AT 7:26 AM

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