The throttle position sensor has nothing to do with idle speed. In fact, 800 rpm is perfect. 1,000 rpm is high enough to result in an uncomfortable clunk when shifting into drive or reverse. Check on the emissions sticker under the hood. Idle speed used to be listed on that, but now it is computer-controlled and is not adjustable, so it might not be on that sticker.
The only thing that can cause idle speed to be too low is if the battery was disconnected or run dead. The engine computer needs to relearn "minimum throttle" before it will know when it must be in control of idle speed. All the other fuel trim data and sensor parameters will be relearned while you are driving without you even noticing, but relearning minimum throttle requires that you meet a very specific set of conditions. To do that, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.
You can also connect a scanner to view live data, specifically, target idle speed and actual idle speed. If the two are the same, everything is working properly. You can also look at "idle steps". That will be a number between "0" and "256". For a well-running engine, step "32" is typical. With one cylinder misfiring, you will find it closer to step "50" to keep the idle speed at the desired speed. If it is at step "0", minimum throttle has not been relearned yet.
Jul 2, 2018 at 9:06 PM
