I took my impala to the dealership for an oil change and the check engine light was on. Turns out the valve was stuck open. When I left I noticed the car was running worse than when I took it in and felt like it was going to stall out at traffic lights. I took it back and they looked it over but couldn't find a problem. They've kept it for more investigation and mentioned it might be the motor mount. It seems too coincidental to me that the motor mount would suddenly go bad right after they worked on it. Should I be suspicious?

 

If they suspect motor mount, put it on the rack.