Check for diagnostic fault codes. The Engine Computer compares various sensor readings under various conditions to check their operation. As an example, after the engine has been off for a specified period of time, the coolant temperature sensor and the intake air / battery temperature sensor should be at the same temperature. If they don't agree, the computer has to determine which one is wrong, then it will inject an approximate value from memory and run off that. The computer might be using the intake air temperature sensor as a backup for the coolant temperature sensor.
There is a specific range of acceptable voltages from every sensor, usually between.5 and 4.5 volts. Outside of those values, the Engine Computer will set a fault code in memory. The sensor's reading can be wrong, but as long as it remains within the acceptable range, the computer will believe it. This is where reconciling various readings can help it detect a problem.
If there's a problem wth the intake air temperature sensor, unplugging it will cause the computer to use a backup strategy calculated from other sensors and run as well as possible off of those values.
Tuesday, March 9th, 2010 AT 5:21 PM