1. Air pockets in the coolant (Lots of them, big ones) from not bleeding system before letting you take it home. Will also explain erratic idle, AND need to add coolant, and sparatic overheating.

2. Fast idle valve (under inlet on throttle body) needs "screwed" back in. Common issue-also explain only erratic idle, but NO coolant issue.

3. A Warped/ Cracked head also will explain loss of coolant, but will overheat, smoke, and have odd idle. (see #2). Check oil and antifreeze color..if either one appears like Chocolate milk...TAKE IT BACK! ITS NOT FIXED.

- Check what I listed....looks like whom ever did the work for you, wasn't very thorough. The head "should" have been checked by a machine shop considering it may have been overheated, or falsely assumed as a gasket when it was a warped/ cracked head.

ALSO-Anytime you coolant system work, the coolant system needs "bled." (Run the car from a cold start with cap off for about a 1/2 -1 hour, adding coolant anytime it gets low. It WILL bubble out, appearing to be boiling, ITS NOT. When it stops bubbling out, no more air pockets.) Newer cars have bleeder screws, yours does not. So disregard about that whole bleeder thing.

As for the fast idle valve, its common, it was needing serviced on my car and I had no idea, until an unsuspecting source mentioned it. And we all were like...OH YEAH! ...3 Idle air valves later....Oooops! But that's also something to check if your idle doesn't smooth out.