My '00 AT has developed a weird idle on cold startups. It sounds like it's gonna stall for a few seconds, then idles good for a few, then sounds like it's gonna stall again for a few seconds, then recovers...and it repeats until the car is warmed up. When at "warmed" temp, it idles fine and runs perfect. No SES lights had come on until yesterday. I pulled the code and it was an 1126 "Thermostat" malfunction. Cleared it and it has not reappeared after driving it today. When I pulled the code yesterday while the car warming up and doing the weird idle, I observed the one of the o2 sensors not reading properly on the live data.

If it was a bad o2 sensor, would it matter if the car was cold or warm? Anybody have any similar symptoms or tech support. Appreciate the help.

 

You may very well have a bad o2 sensor. During cold starts, your Max will run rich as a safety precaution, till it warms up to normal operating temperature. This is normal on almost every car for a warm up procedure. I would suggest you have your o2 sensor checked/replaced.

 

It’s not a safety precaution. 1126 is your thermostat function.

 

The new cars depend on the thermostat to operate. Some of the thermostats stay open to prevent it from overheating. Maybe it is open and it is taking longer to get to opertaing temp.

 

That's exactly what's happening here.