idle speed

That's typical of a vacuum leak. First check all of the vacuum hoses for a leak or break. There can also be a leak in the intake manifold gasket, throttle body base gasket, and at the throttle shaft bushings. One way to find those is to spray water around the gaskets while the engine is running and still cold. The speed will drop and you might see the water get sucked in when you spray the leak. Also check if the throttle body assembly is loose. On older models sometimes the base gasket shrinks and the throttle body bolts need to be tightened.