I don't know what that did, but it sounds more complicated than it needs to be.
The Engine Computer needs to know when your foot is off the accelerator pedal, then it takes a voltage reading from the throttle position sensor and puts that in memory. That is the minimum throttle voltage it needs to see from then on. It will adjust idle speed whenever it sees that voltage.
The first step in knowing when to take the reading is it needs to see higher-than-normal intake manifold vacuum. That will occur if you snap the throttle open and quickly release it, but there's no guarantee you released it fully. That high vacuum would only last for two or three seconds. Coasting from highway speed is the only way to make that vacuum stay high for seven seconds. Pressing the brake pedal will cancel the relearn procedure, and pressing the accelerator pedal will cause the TPS voltage to vary. That will tell the computer your foot is still on the pedal, and it should ignore the relearn request.
No two sensors are ever exactly alike. When the TPS is replaced, if the signal voltage at idle is lower than that of the old sensor, the new, lower voltage will immediately be put in memory. If the voltage at idle is higher than before, the computer will assume you're holding the accelerator pedal down a little. It will learn the new value the next time you coast for seven seconds.
For most people, the seven-second coast procedure is a normal part of daily driving, so idle speed problems aren't a concern. More problems are caused when people start blindly replacing multiple parts that need to be learned by the Engine Computer. It does that by comparing the characteristics of a single new part to those of other sensors and operating conditions. Replacing numerous parts at the same time can confuse the process.
Idle speed can also be too high. Most of the time that is due to a vacuum leak, but it can also be caused by the computer reacting to an incorrect sensor signal. For example, a coolant temperature sensor that is reporting a temperature that is too low will cause a high idle speed. You need a scanner to view live data to see what is happening. The computer places the automatic idle speed motor to one of 256 "steps". Each step rotates the armature a small amount, and that retracts the pintle valve to expose more of the air passage around the throttle blade. For a properly-running engine, step 32 is typical. With a single-cylinder misfire on a V-8 engine, step 50 is about what can be expected to bring idle speed back to where it should be. The AIS motor has enough control to maintain desired idle speed with six cylinders disabled on a V-8 engine.
When idle speed is wrong, you need to know the step the computer has placed the AIS motor at. If it is "0", minimum throttle hasn't been relearned yet. If the step is real low but idle speed is too high, the computer is trying to bring it down, but without success. If the step is very high, the computer is trying to overcome the result of whatever is causing the speed to be too low.
Monday, January 23rd, 2017 AT 4:34 PM