My 2005 Buick Century (3.1L V6) starts but quickly shuts off at idle. I have to rev up the RPMs for about 10 to 15 seconds to get it stay on at idle. By reading a post from another forum, I learned it has the symptoms of a faulty (or dirty) Intake Air Control (IAC) valve. The strange thing is, the problem is more prevalent when I start the car in the dark when the headlights automatically turn on. It rarely happens in daylight. Could the problem be a combination of things, including a weak battery? Also, I started having this problem after I took the car to a state-run emissions facility. When the inspector plugged a diagnostic device into the car’s computer port, could he have accidentally messed up some embedded programming instructions in the car’s system? I had the fuel pumped replaced about 3 months prior.
It could very well be a dirty/bad IAC valve.
When you start the car when it’s dark and the headlights come on automatically, this causes the charging system to put a load on the engine.
Any load put on the engine at idle is controlled by the IAC valve.
So, that would be the first thing I would suspect.
Tester
Thank you, Tester.
I replaced the IAC valve. The car starts fine in the headlights-on condition.
You helped me save a bundle of money on a professional mechanic.
Hello Tester,
I thanked you too soon. My car was running fine during the morning commute. But towards the end of my afternoon drive home, the engine started racing. It had the opposite problem than before. Could something else cause the IAC valve to fail? Or, do you think I had the misfortune of getting a defective one? Any thoughts or ideas will be appreciated.
jmcarc
If the engine races with your foot off the accelerator, you got a bad IAC valve.
Tester