Does the car have a MAF? (Not familiar with the setup in that car)
If so, try cleaning it. I’ve heard about freshly oiled K&N’s causing similar issues…
More air requires more fuel. Same as when the temperature drops, the air is more dense which requires more fuel.
Also did you remove the honey comb from your MAF?
that is not a good idea, that screen is there to straighten out the Airflow across the MAF. Most of time removing that leads to rough idles and terrible drivability (speaks specifically doing this on the 3800)
Exactly what I was gettin at.
Its all in your head