Many years ago I had a similar problem with another brand of car (which I won't mention) and we later found out it was the ecu that was defective.
You might also want to see if the a/c is fully charged. My problems started with low freon and the clutch for the a/c engaging intermittently when a/c was on.
Later on the car's poor preformance was attributed to damage to the ecu. Don't know if the two were ever related but thats my experience.
BTW I ended up selling the fkn car.
Hope this helps,