2007 TrailBlazer rough idle when cold

[monteheeren]

My 2007 TrailBlazer with 84K stumbles for 25 seconds
when I start up cold. After 25 seconds I hear a click and
then it runs perfect. Drivin me nuts. No engine codes present.
Have new plugs, new O2 sensor, new thermostat.
Any ideas would be greatly appreciated.

[maxwedge]

You may have no codes but a full scan looking at all inputs, pending codes and misfire counts may pinpoint the issue.

[monteheeren]

MaxWedge,
Thank you for your reply. I need to have it scanned.

[monteheeren]

Doing more diagnostics. Found out my TrailBlazer has a secondary air pump that pumps air into the exhaust manifold thru a control valve mounted on side of the head. On cold start up the pump pushes air into the exhaust manifold for 30 seconds to help 02 sensors warmup more quickly. I pulled off the hose on the air control valve on cold start and it pushes a lot of air for 30 seconds. If I unplug the control valve the engine starts good but has a check engine light on. Don't know if this is normal or not to have the engine run rough for 30 seconds on cold start up. Anyone else have a similar experience?

[maxwedge]

That is not the function of the air system,the o2sensors have their heaters built in. Possible the check valve is corroded and stuck.

[monteheeren]

I tried 2 check valves with the same problem.