First of all, when you start the engine, the idle speed is supposed to go up to around 1500 rpm for a couple of seconds, then come back down to around 800 rpm. That "idle flareup" proves the Automatic Idle Speed motor is working and the computer has control of it. On some engines that idle flareup won't occur if minimum throttle is lost from memory.
The second test involves disconnecting a fuel injector while the engine is idling. Engine speed will drop at first, and the computer will respond by bumping it back up. The same thing will happen if a second and third injector is unplugged. You can do the same thing by shorting out a spark plug wire, but don't do that for long because the unburned fuel will overheat the catalytic converter very quickly.
If you think minimum throttle has been lost from memory, the relearn procedure is very complicated. :) Drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals. That will meet the conditions for the computer to know your foot is off the gas pedal. It will memorize the voltage reading from the throttle position sensor. From then on, whenever it sees the same voltage, it will know it must be in control of idle speed. Until then, the engine will typically stall at stop signs due to idling to slowly. The problem can be overcome by jsut holding the gas pedal down 1/4".
Saturday, June 19th, 2010 AT 5:32 AM