I have a stock '87 GT 5-speed and a stock '88 GT auto. The '87 has had a rough idle. The '88 has a smooth idle.
I am trying to check vacuum lines on the '87 for a leak. When I pull the small line off the top of the EGR Valve on both cars, I hear and feel no difference in motor operation.

What should the correct normal result be when the small vacuum line is removed from the top of the EGR Valve on a normally operating 2.8L?
Would it depend on engine temp, or other variable?

Thank you for the help on this.

If you aren't getting a code 32 when you drive, then the vacuum lines on both are probably good. To test the EGR valves, with engine off and cold, disconnect the vacuum line at the valve, underneath press up on the diaphragm with your fingers and cap the port with your finger. Hold your finger on it for about 30 seconds while feeling for the diaphragm to leak down. If it doesn't leak down, the valve is good. You can do the same test using the vacuum line by disconnecting it at the EGR solenoid and capping it instead of at the port on the valve. That way you test the line and valve at the same time.

The reason you don't feel any vacuum from the line when you pull it off the EGR valve is because there isn't any applied until commanded by the ECM. The ECM only does this under certain conditions like part throttle cruise. Once the right conditions are met, the ECM triggers the vacuum solenoid to open, allowing vacuum to be applied to the line you're trying to test.