Just bought 2004 4runner sr5 - issue CEL on, VSC TRAC off and engine overheat

What is your question?

Just bought 2004 Toyota 4runner SR5 156k miles/1 owner from dealer last week for my teenage son. Highway test drive fine and dealer showed me an inspection from Toyota dealer. He mentioned that sparkplug coils and plugs changed by local auto shop. My son drives for a week, the Check Engine Light, Air Pressure low indicator and VSC Trac and VSC Off comes ON. Previous day they all came on and went away. I take it to the dealer and while driving saw that the engine temperature was going up constantly towards the top. Dealer checks code with OBD tool and said it shows spark plug issue and wants to take it back to the mechanic and got appt next week. Changed fuel cap, removed positive battery plug, the CEL went AWAY but VSC TRAC off comes on when i put the car in reverse or drive mode Coolant overflow tank empty, filled it and drove 4 miles, next day it was all the way down. Do I have 2 issues- VSC OFF, CEL and engine overheat or they all related to the sparkplug issue? Pls advice.

What makes this problem better or worse?

engine issue

How long has your 2004 Toyota 4Runner had this problem?

1 week