If the throttle position sensor was defective it would have set a diagnostic fault code. No two sensors are ever exactly alike. By replacing it you introduced a new variable and the Engine Computer hadn't relearned its characteristics yet. Until that happens it relies more on other sensors to calculate fuel needs so it can act differently.
There's two things to look at with a high idle speed. The first is vacuum leaks. Intermittent ones can be tricky to find. If you can get it to act up while the engine is still cold, you can try spraying water on the vacuum hoses and intake manifold gaskets. Watch for where it gets sucked in or slows the engine speed. You can also connect a smoke machine to inject white, non-toxic smoke at 2 psi into a vacuum hose, then watch for where it sneaks out.
The second thing is to connect a scanner to view live data and see where the Engine Computer is placing the idle speed motor. That will tell you if it is trying to increase idle speed in response to something or if it is trying to decrease idle speed and not having any luck.
Jul 23, 2013 at 10:30 AM
