I believe those pending codes refer to the downstream instead of the upstream O2 sensor so I would focus upon it. That would make sense that it dies after cold idling for a minute or so because that would be in the time period that the ECM is trying to go from open to closed loop mode and bad reading from the downstream sensor would start to be used as it enters closed loop mode.

Rodger

 

Thanks. The p0133 is for the upstream sensor and the p0137 is for the downstream. I’m going to replace the downstream today and see what happens

 

Did the seller state why the car had been sitting? Maybe some direction with that info.

How does the fuel trim look now compared to before you replaced the O2 and MAF sensors and plugged the vacuum leaks?

 

The car needed a steering rack, brakes, exhaust manifold gasket, and a couple other things. He didn’t have the money to put into it.

The fuel trims are a lot better now then they were. They are staying +/- 15ish mostly staying +/- 10 where as before it was running +25 and up at idle

 

Replaced down stream sensor with an gm one. Still misfiring and stalling at on cold start up. Fuel trims are showing rich. Long term was up to -25ish any ideas?

 

Have you checked the intake manifold for cracks? How is the intake manifold gasket?

 

Have you checked the intake manifold for cracks? How is the intake manifold gasket?

Did you replace the MAF with an OEM AC Delco sensor or is it aftermarket?

I have sprayed around the intake with brake clean. I have also smoke tested the motor.

The MAF was not oem. When I noticed there was no change I ended up putting in the factory one

 

Maybe a clogged cat.

 

So I ended up replacing the upstream o2 sensor again for the third time but this time I used a gm genuine sensor and all the problems seem to have gone away

 

Thanks for the update and really good to know! Wondering, what brand oxygen sensor were you using? This is some good information for other ATS owners out there to be aware of.