question about idle

[p51speed]

my truck idles at 1600 (which is to high) but then is drop down to about 1400 for a second then picks back up. now I am not a mechanic but i feel if i can figure out whats wrong i can fix it . has anyone have a any ideas?

thanks in advance.

by the way the truck is a 1987 pathy v6 4x4 thanks

[smj999smj]

Somethings to check... Is the coolant reaching normal operating temperature? If not, you may have a thermostat stuck open. IIRC, there's a thermal wax element that controls the cold start fast idle that is warmed by coolant. It called by bad or there is a restriction impeding the flow of coolant through it's housing, located on the throttle body unit.

[p51speed]

I will replace the thermostat and check back in with you thanks.