i have a 89 toyota 4 cyl 5 speed. i rebuilt the motor about 40,000 miles ago. it ran perfect up until about ten thousand miles ago. it started out idle surging however i fixed this by changing out the iacv. the idle will still idle high after warm up now though for a short period of time and then wont do it again until the truck is shut off and cooled down and started back. i have also noticed after shut off the truck is pushing antifreeze into the overflow tank and out the hose. i have already replaced the cap, thermostat, and fan clutch and replaced the iacv, mass air, temp sensor, cold start injector and a few other things when the idle was surging before this problem. any ideas?