Why is my battery light on?

All the scanners I ever used showed it as a voltage, but regardless of how it's displayed you want to see it change smoothly as you slowly press and release the gas pedal. If there is any place where the wiper makes intermittent contact the reading will momentarily bounce to 100 percent or 0 percent. That is what sets the fault code.

Also, scanners and digital voltmeters have a delay between taking a reading, analyzing it, and displaying it. For that reason a glitch can occur so quickly that you don't see it but the Engine Computer will. In that case, since the readings are correct most of the time, you know the wiring is okay. Then you have to just replace the sensor.

No adjustment needed or possible. The Engine Computer has to relearn "minimum throttle" after the battery was disconnected before it will know when to be in control of idle speed. Until then, the engine may not start or it may stall when approaching stop signs, unless you hold the gas pedal down 1/4". You also won't get the "idle flare-up" to 1500 rpm at engine start up. The conditions for the relearn to take place are driving at highway speed with the engine warmed up, then coasting for at least seven seconds without touching the pedals. At that point the computer takes a voltage reading from the TPS and puts it in memory. It knows by those conditions that your foot is off the gas pedal. From then on, any time it sees that same voltage, it knows it has to watch and control idle speed.

No two sensors are ever exactly alike. My understanding is that if you install a new TPS with a lower voltage at idle, the computer will see that and immediately learn that as the new minimum throttle voltage. The problem is when that new sensor's lowest voltage is higher than the old sensor's lowest voltage. As far as the computer is concerned, it thinks you haven't fully released the gas pedal so it lets you control idle speed. Mechanically, nothing has changed with the throttle blade so now the engine may idle too slowly and stall or be hard to start. If that happens you just have to do the seven second relearn again on the highway.

Yup, do the relearn. If that doesn't help, the scanner has a test that will run the idle speed up and down in 200 rpm increments to see if it's working. If it's not, that motor could be bad but it's more likely the air passage is plugged with carbon. That's not too common anymore thanks to better fuel additives.

Then you'll want to find a scanner to test the automatic idle speed motor. It's not a regular motor as you would think of with brushes but it does have an armature. Rather than spinning, it's a stepper motor that is set to various positions when the computer pulses the coils with voltage. As the armature turns, it's on a threaded shaft that retracts a pintle valve to open an air passage around the throttle blade. At the same time the computer lengthens the time it holds the injectors open. That's how it controls idle speed.

There's two things you can do with the scanner. The first is to view the number "steps" the computer has requested. There's 256 steps from 0 which is fully closed to 256 which is wide open. For a properly running engine you'll typically find it at about step 32. Step 50 is about where you'll find it with one misfiring cylinder on a V-6 engine. You can ground out one spark plug wire, then watch what happens to the steps. If it's on "0" or if it doesn't change, minimum throttle hasn't been learned. That can happen if part of the brake light switch isn't turning off, or if there is one of any of the fault codes stored that will inhibit the relearn procedure.

The second test is under the "actuator" menu. It lets you run the engine speed up to 2000 rpm in 200 rpm increments. If the steps go up but engine speed doesn't, the air passage is plugged with carbon or the motor isn't turning. Plugged passages used to be common on the 3.0L engine but it's pretty rare today.

You can also unbolt the idle speed motor and if you squeeze the valve really hard, it will retract about 1/4". If you reinstall it like that, idle speed should be too high and it will slowly come back down as the computer pulses it over as much as ten seconds. If you do remove it, be sure the torx bit driver fits snugly or the bolt heads can be rounded out. They're installed with Lock Tite and will come out hard.

What do you mean by "idles bad"? Does it have a misfire? If it's setting a related fault code, that can inhibit the relearn from taking place. Or do you mean it's just running rough because it's idling too slowly?

You can try holding the brake pedal up with your toes while you do the seven-second coast. If that works, the brake light switch is defective or out of adjustment. Next, remove the idle speed motor and retract the valve by hand. It will move hard but not so hard that you have to squeeze it in a vise.

I'm working with someone else who has the same problem on a Jeep, and he solved the problem by removing the idle speed motor and cleaning the valve and passage with carburetor cleaner and a tooth brush. I wouldn't have expected that little carbon to be a factor but there's no arguing with success.

You need to do the relearn procedure because either the battery was recently disconnected or the voltage at idle from the new TPS is higher than from the old sensor. No two sensors are ever exactly alike. As an example, if the lowest voltage from the old sensor was 0.72 volts, the Engine Computer will know it has to be in control of idle speed whenever it sees that voltage. If the lowest voltage from the new sensor is 0.79 volts at idle, the computer will never see the 0.72 volts it is expecting so it assumes you're holding your foot on the gas pedal and it is going to let you be in control of engine speed.

To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals.

Then you need to use the scanner to view the idle "steps" the computer has placed the idle speed motor to. If it is "0", the relearn hasn't taken place. Try holding the brake pedal up with your toes while doing the coasting procedure. If it is around 32 or so but the speed is too low, suspect the air passage around the throttle blade is plugged with carbon, but we don't see that too much anymore.

You can also use the scanner to run the engine speed up to 2000 rpm in 200 rpm increments. That will verify the new idle speed motor and wiring are okay.