Buick Mystery

2006 LaCrosse stalls at random when a/c is on under 30 mph. it can go all day without a stall or can stall 10 times on a short trip. diagnostics shows nothing and every mech who has seen it is stumped including dealer. car restarts immediately and has no other symptoms. is it haunted or what??? Heeeeeelp!!!

If the engine stalls when you release the accelerator, have the Idle Air Control valve checked out.

The IAC valve controls the engine idle speed depending on the load imposed on the engine. So for example if you’re turning the steering wheel with your foot off the accelerator the IAC valve bumps the idle speed up so the engine doesn’t stall from the load imposed on the engine from the power steering pump. The same thing happens when the AC is on. When you release the accelerator the IAC valve bumps the idle speed up so the engine doesn’t stall from the load imposed on the engine from the compressor. If the IAC valve fails to go to the proper position when the AC is on, the engine will stall when the accelerator is released.


I don’t know what the name of the tool is but see if they have one of those devices that they plug into the diagnostic link, then when it stalls you push the button and it captures all of the relevant information for the past minute or so to find the problem. If it doesn’t show up that way, I’d be looking at a fuel regulator or fuel pump/relay or EGR issue. Just IMHO.

Start throwing parts at it, start cheap with a pcv valve.

You could have either a dirty throttle body, but usually you notice this because the gas pedal will stick when you first step on it, but if you have throttle by wire, you won’t feel that. Or someone could have “adjusted the idle” by turning the idle stop screw.

Either one of the above would keep the computer from getting the signal that your foot is off the gas so it won’t know to take over the idle. It will appear that the IAC isn’t working right, but it can’t work right if it never gets any signals from the computer.

Bing, it’s generic name is a “Scan tool”. They can be bought at any parts store, and the more you pay is generally the more information it’s capable of providing. But since parts stores scan codes for free, and any tech worth his/her badge is going to download his/her own reading anyway, unless one plans to do his/her own work I’m not sure it’s worth buying one.

What Bing is refering to is called a “CO-PILOT”. http://www.todrive.com/home/12930429-615/letters-dealer-installs-co-pilot-to-aid-diagnosis.html

The driver pushes a button when the problem occurs and the Co-Pilot records the data so it can be down-loaded at a later time to determine what’s causing the problem.


Cool. I’d heard of these, but not used one, and had forgotten of their existance. I wish there were one I could plug into my neural network…