QuestionThe car starts fine but idles high, about 1,500 to 2,000 and almost sounds
like it has a miss. It revs fine and sounds good at higher RPMs. Check engine
light is NOT on. Changed plugs, didn't help at all. I don't want to just start
replacing things randomly.
AnswerHi, Michael. There are a few things you should check.
Verify the throttle cable has some slack in it; i.e. it isn't holding the throttle open. If there is no slack, adjust the cable.
If the throttle cable is okay, you should also check the throttle position sensor. It'll be difficult for you to do this accurately without a scan tool that can display the percent of throttle opening. However, one quick test you can make is, with the engine running, grab the connector for the throttle position sensor and wiggle it back and forth. If the engine idle returns to normal when you do this, it's a safe bet the throttle position sensor contacts are dirty. In such a case, you'll need to replace the throttle position sensor.
In the vein of less likely conditions, your coolant temperature sensor may be reading incorrectly, causing the engine control module (ECM) to think the coolant is cold when it is not.
You may also have a condition whereby air is entering the engine without passing through the throttle body. For the rpms to be this high, it would normally be quite a large vacuum leak, and I'd also expect the check engine lamp to be on, so I don't think this is your issue.
Lastly, your idle control actuator may be malfunctioning, but once again, the ECM would typically notice it cannot return the engine to idle, and set a corresponding DTC.
