That's the EGR intake pipe. There's a passage in the manifold for the gasses coming from the exhaust; there's a solenoid that controls whether the gasses are allowed into the incoming air. The sensor on top is a temp sensor.
From a tuning article on the LT1, so physical objects are different, but the concept is the same:
"This readout tells you when the Exhaust Gas Recirculation (EGR) system is working. The EGR valve is opened to allow exhaust gasses to enter the combustion chamber with the air and fuel. This reduces the combustion temperatures, and reduces the formation of oxides of nitrogen, a pollutant - not to be confused with nitrous oxide (N2O) which is an aphrodisiac to the bottle-fed types among us….
The EGR system typically does not work at idle, and does not work at WOT. So it has little impact on performance. If the system is leaking, it will hurt performance though, and it tends to heat up the back corner of the intake manifold, but that is not of interest to the ScanMaster.
The EGR valve is turned on by applying vacuum. The vacuum is controlled (turned on and off) by the vacuum solenoid. The solenoid is "pulse modulated". The vacuum solenoid is switched on and off rapidly, and the more "on" time is has, the more EGR is flowing. The ScanMaster reads the pulse modulation "percentage" or the percent of the time (out of 100%) that the EGR valve is (supposed to be) operating. This is not a measure of how much EGR is actually flowing, only of how much it is supposed to be flowing. If there is a problem elsewhere in the EGR system, the ScanMaster doesn't know about it.
Watch the readout. Most likely, if you are cruising along, and push the throttle a little firmly and a little rapidly, the EGR value will jump from "0" to "100". You don’t see values in between too much, but it is possible.
The EGR valve is the big black donut shaped device on the back of the intake manifold. Exhaust gas flows from a tube on the #8 exhaust manifold runner, to the back of the intake manifold. The EGR valve controls how much, if any, exhaust gas it admitted to the intake manifold. The solenoid that activates the vacuum is located on the drivers side of the intake manifold, on a clip near the back. The source of vacuum is a port on the drivers side of the intake manifold, near the middle by the PCV valve."
[RICHR]
