Engine Mechanical problem
2002 GMC Sierra V8 Two Wheel Drive Automatic 109000 miles
When the outside temperature is about 40F degrees or below, my engine idles really rough until it is warm. It recently started coding P0300(random misfire). This problem started last winter. Ran throughout the summer with no problems at all. Started up this morning at 25F degrees with a rough idle. I gave it some gas to increase the RPM for about a minute, then about one mile up the road at a stop light, it was still idling a little rough.
In the past, I seem to remember the idle staying above 1000 RPM for a good amount of time on cold mornings. However, now, it starts up at about 1100 and quickly, within 20 seconds, starts to ramp down to 500, where things get rough.
Here is what I have done so far.
During the summer, I replaced all spark plugs and I recenlty installed new plug wires. Made no difference.
I replaced the coolant temperature sensor. No improvement.
As suggested by a friend, I placed my old Coolant temp sensor in my freezer for about an hour to cool it down. I then plugged it into the connector while the engine was still warm. The engine did not want to start when I cranked it. I held the gas pedal down a bit and finally got it to start and the idle was fine. Not sure how to interpret those results. Friend thinks it must be the computer.
I wanted to replace the mass airflow sensor since I read that it has fixed the issue for others, but everyone keeps telling me not to unless there is a code for that.
Some think it could be a vaccuum leak. There are few vaccuum hoses on this engine and they all seem to be ok. Perhaps it could be the intake manifold gasket.
What do you think?
Wednesday, December 9th, 2009 AT 2:15 PM