Link:
https://troubleshootmyvehicle.com/gm...gr-valve-tests
TEST 1: Continuous Vacuum To EGR Valve
EGR Valve Stuck Open. Diagnosing A Stuck Open EGR Valve (GM 4.3L, 5.0L, 5.7L)
The fuel injection computer is the one that regulates the opening and closing of the EGR valve thru' the application and release of vacuum (through a vacuum solenoid).
One side of the EGR vacuum solenoid (the one that has only one vacuum inlet port) connects to the vacuum port labeled with the letter J on the throttle body.
Ezoic
In case you're wondering, the letter J is embossed above the vacuum port on the throttle body.
The other side of the EGR vacuum solenoid has 2 ports. One is a vent port (that vents vacuum to the atmosphere) when the engine is idling. The other port connects to the EGR valve and should only have vacuum when the PCM commands the solenoid to activate.
So, the first thing we'll do is to make sure that vacuum is not being applied to the EGR valve when the engine is just idling.
These are the test steps:
1
Disconnect the vacuum hose that connects to the EGR valve vacuum port. Leave the other end that connects to the EGR vacuum solenoid connected to it.
2
Connect a vacuum gauge to the vacuum hose you just disconnected from the EGR valve.
NOTE: If you don't have a vacuum gauge, don't panic. You can still check to see if vacuum is present in the vacuum hose.
3
Start the engine and let it idle and check to see if the vacuum hose has vacuum.
The vacuum hose that connects to the EGR valve should not have vacuum.
Let's take a look at what your test results mean:
CASE 1: Vacuum WAS NOT present. This is the correct and expected test result since manifold vacuum should NOT be present when the engine is idling.
The next step is to remove the EGR valve from its place on the intake manifold and make sure it's valve pintle is not stuck open. For this test, go to: TEST 2: EGR Valve Pintle Stuck Open.
CASE 2: Vacuum was present. This is a problem, since vacuum should not be present when the engine is idling.
This could be caused by one of two possibilities, either the EGR solenoid is defective or the vacuum hose is attached to the wrong port on the EGR solenoid.
Resolving this ‘continuous vacuum to the EGR valve at idle’ problem will solve the EGR valve and rough idle issue.