2004 Forester XT 180K - NEWLY rebuilt engine, w/new CTS (water temp), plugs, wires, new front AFR / O2 sensor...

 

When cold, car runs poorly - stumbles and hesitates for 1st 1-2 minutes 'til it warms up. No CEL. It's worse w/colder weather we've had the the last week - mid 30's F.

 

It did this BEFORE the Rebuild and After. And it does it on the Stock tune, a Cobb OTS tune, and a Custom -online- tune.

 

Leads me to believe it's an 'Open Loop' issue in the ECU's programming? The front O2 sensor is new - Not the rear, but since they're not used until it gets to Closed Loop, they shouldn't matter?

 

I'm not sure what to log on the Cobb AP but guessing that's a place to start.

 

Thanks for any feedback.

 

Td

Vacuum leak? PCV and breather hoses connected tightly?

Seems like it should be something basic. Checked timing belt alignment?