i had both problems on my 2.6

the overheating issue was a simple coolant reservoir cap ( aka rad cap )

we tested it with a pressure gauge and it would not hold 15PSI like it should. Got a new one for 20 PSI, solved

the high idle problem was easier than i thought. After being stumped for many months, i took out that microswitch with that little wheel near the throttle linkage and upon examining it, it was very oily. So i disconnected the switch going into it and cleanned the leads and made sure the thing is dry. I guess the oil was preventing the thing to work properly. When you put it back, make sure the little wheel rests against the little "clicker " so that it clicks in and stays like that when your car is in P or N. When you are in D or R and press the gas, the little wheel should get off the clicker as the clicker is a signal to keep the RPMS low.