sometimes starts with low idle sometimes starts correctly.

10

Asked by Mar 21, 2013 at 11:31 AM about the 2002 GMC Sierra 1500 SLE Standard Cab SB

Question type: Maintenance & Repair

2002 GMC sierra. sometimes when I start the truck it will idle about 500, then it will run rough or stall. If I turn it off, I
have to turn the key off completely, and restart it will idle at 1000 and run smooth. Sometimes I need to do this
process 2-4 times before it will run smooth. Once it starts and runs smooth it doesn't have any problems. Any idea
on where to start trouble shooting?

7 Answers

please come armed with your OBD diagnostic report (free), 'cause we're shootin in the dark here....first I thought vacuum leak...and I thought to which component...then I thought this thing is gonna trigger alarms regardless...so we've got to figure out what vacuum operated device is being naughty-...also could be electrical, we cannot guess with the info provided.

2 out of 2 people think this is helpful.
10

When I test it is reporting an issue with an o2 sensor but no visible check engine light. When I get home I will give you the exact reading I get.

1 out of 1 people think this is helpful.

Sweet. You will be rewarded with a correct answer.

30,955

Idle air control sticking, it's getting stuck in the closed position for closed loop mode and when it cools and gets restarted in open loop mode it's not resetting to the open position. Its staying shut for a warmed engine to run at 600 rpm but a cold engine will not idle at that rpm. A vacuum leak will make an engine idle high not low unless the leak is enormous and the leak also wouldn't go away. This isn't the only possibility but the most common, most likely, and by far easiest to check/ fix. Pull the old one and soak it in Carb cleaner. $5 bucks for a can of cleaner and 20 minutes of work.

2 out of 2 people think this is helpful.
30,955

Btw O2 sensors will NOT cause a cold start issue, the O2 sensors are ONLY read in closed loop and the engine is ONLY in closed loop once it reaches operating temp which is above 160°F AND the O2 sensors have to be up to temp. It takes roughly 5 minutes for this to happen while letting a vehicle idle on a 45°F day.

i would look in to cleaning mass air flow sensor that would do the job. need to get mass air flow sensor cleaner and let it sit for 30 minutes the install it back walla no more hesitating or sputtering .

Hello friends I have 02GM Sierra and I got no power in my truck I step on gas pedal and it won't go??

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