My car started accelerating by it self. it idles until 3000rpm then stops and idles up and down from 1000 to 2500rpm. i went to my mechanic and he said the antifreeze was leaking from the idle air control valve to the engine. so he put a new gasket. the problem stopped for a few hours and started again. also when i start the car the rpm goes all the way down to 250rpm den back to 500rpm and stays there? please help.

 

It sounds like there is still a problem with the IAC. Might need to have it cleaned and see if that solves the problem. Good Luck!

 

Be sure the coolant is full, because an air pocket in the system can fool the temp sensor.
Also be sure there is a little slack in the throttle cable.

Your post is a little confusing;
Is the surging idle problem at cold start fixed?
Is the low idle speed at start up the problem you're trying to resolve?

 

well now its not accelerating by it self . so i guess that is good. but now everytime i start the car, the rpm goes all the way down to 250rpm then goes back up to 500rpm. usually my car regularly idles at 800rpm before this problem started . its way too low now? why?

 

for the low idle, I would first try to clean the screen on the IACV, as well as clean the throttle plate area with a toothbrush and Berrymans B-12 carb cleaner. You can also spray some carb cleaner thru the 2 air ports infront of the throttle plate.
Those throttle plates can also stick a little bit at cold start when you first step on the gas, if there is a ring of crud built up around the throttle plate.
Throttle plate cleaning pic; [with my wifes toothbrush]