Yes, the MAF is new. As are pretty much all the sensors except so far the O2 sensors.

 

At least you’re narrowing it down.


pardon me, if you’ve already done so but have you done a full battery lobotomy?

 

Latest from the tech/mechanic I have working on the problem is that the computer was never updated per an obscure TB tech bulletin that relates to rough idle on start. Planning to get a local GM service facility to perform that update. Although i swapped out the computer module once with a refurb unit it is possible that one was not updated either. It was not a mandatory update sooooo..... more to come :)

 

Finally got an appointment at a Chevy dealership service center. They've had the car for 3 days now. I filled them in on the history of the problem, parts I replaced, my local mechanic's efforts and conclusions. They called me today to ask if the engine has ever been replaced. (It's a salvage title car totaled by the insurance company at around 6K miles after new in 2010 or 2011). So I don't know if the engine was replaced but the vin calls for a 2.4l engine which is what it has. So all indications are that this dealership service dept. is also baffled by the problem I am hoping they have a brainstorm and figure this out before it costs me much more. That's it for now but I expect a final report soon.

 

Thank you for the update, we’ll wait

 

Didn't read if you had replaced the air filter? although, it wouldn't explain why open loop causes the issue to go away. I think that may be the biggest clue to this problem. If they haven't figured it out when you get the car back (or ask them to) try the 02 sensors since it's the only part that hasn't been replaced and that is the part that tells the computer if the air/fuel ratio is correct after it leaves the combustion chamber. I know you had someone test for leaks but maybe there could be a small one in the intake manifold that was missed? worth a second look anyway and lookin is free!

 

Hi and thanks very much for the suggestions. The air filter was the first thing I replaced when I got the car. But the o2 sensor has been on the back of my mind as the only thing I haven't yet replaced. One mechanic told me the O2 sensor is not used during closed loop to determine mixture so have not pursued that. I will though, as you suggested, bring it up with the dealership service dept. that is now trying to diagnose this. Thanks for the reminder :)

 

That mechanic has it backwards! Closed loop means that the sensors are providing feedback, Open loop the computer relies on it's own tables.

 

You are correct but it was my error. I meant to say open loop in my comment. My mechanic was correct. And the problem resolves once it goes into closed loop.

 

i really did not expect this car to present the biggest technical challenge of the century to the automotive industry but here we are. the local Chevy dealership has now had the car for over a wek and can't figure out what the bloody problem is. After they called me to pick my brain on the history of the problem and the car, authorized an additional hour of diagnostic time in hopes we will get some answers. Today....no call from them which is making me a little concerned. When do i pull the plug on this?