# Idle speed effects heater output **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [January 1, 2008, 7:55pm UTC](https://community.cartalk.com/t/idle-speed-effects-heater-output/8908 "2008-01-01T19:55:40Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Davidmnman](https://avatars.discourse-cdn.com/v4/letter/d/e495f1/32.png) [@Davidmnman](https://community.cartalk.com/u/Davidmnman)\ **Post date:** [January 1, 2008, 7:55pm UTC](https://community.cartalk.com/t/idle-speed-effects-heater-output/8908/1 "2008-01-01T19:55:40Z")
2002 Chevy Venture, 149k miles. why does it blow cold are out of vents when car is idling. even if engine temp is up to nornal temp. if I press on gas and bring RPM.s up then hot air comes out. but soon as stop at light or when I start it in morning to warm up engine gets hot but does not blow out hot air. I was told that my head gasket was leaking slightly to outside but no sign of coolant in oil yet. could that be it. I do not notice much anti freeze leaking out on to floor. What could it be. One person said maybe heater coil has air pocket. and needs to be burpped. I took off radiator cap and notice cap has oily stuff on it. Any suggestions ---
**Author:** ![mcparadise](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mcparadise/32/32_2.png) [@mcparadise](https://community.cartalk.com/u/mcparadise)\ **Post date:** [January 1, 2008, 8:55pm UTC](https://community.cartalk.com/t/idle-speed-effects-heater-output/8908/2 "2008-01-01T20:55:57Z")
The vacuum-controlled air temperature flap in the HVAC system is moving when it shouldn’t. There is high engine vacuum at idle and lower vacuum as you open the throttle. I think you have a vacuum leak somewhere. It sounds like this is the LEAST of your problems. ---
**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\ **Post date:** [January 1, 2008, 10:08pm UTC](https://community.cartalk.com/t/idle-speed-effects-heater-output/8908/3 "2008-01-01T22:08:18Z")
MC is right. I suspect the vacuum issue as well, but the air block is a possibility, if less likely. However before bothering with the heat, you need to get the head gasket issue addressed and the apparent coolant leak.