what engine do you have?
i think the idle is a separate issue..this may be the iac[idle air control]this is located on the side of the throttle body..sometimes you can remove this and clean it with carb cleaner and it will work fine..though you may need a new one
See Figures 1 through 6
CAUTION When draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.
FIG : Fig. 1: To remove the thermostat, loosen the thermostat housing mounting bolts ...
Fig. Fig. 2: ... then lift the housing off of the intake manifold, thereby exposing the thermostat (arrow)
Fig. Fig. 3: Remove the old gasket from the housing or the intake manifold (depending onto which surface it is stuck)
Fig. Fig. 4: Grasp the thermostat by hand and pull it up and out of the intake manifold
Fig. Fig. 5: When installing the thermostat on 1.3L and 1.6L engines, ensure that the air bleed valve (1) is facing toward the front of the engine
Fig. Fig. 6: On 1.8L engines, when installing the thermostat, be sure that the air bleed valve (2) and the matchmark (3) are aligned
first,,check all vacuum hoses for leaks..but the problem may be the iac[idle air control]valve..this is located on the side of the throttle body,,sometimes you can remove these and clean it with carb cleaner and it will work fine,,though you may need a new one
thanks...sorry i don't have a picture of this,,but it is located on the side of the throttle bode,,kinda looks like a little electric motor