EGR/EVR valves

EGR's get ported vacuum from an off idle port in the carburetor. And, they usually have a electrically controlled solenoid valve to lock out the EGR during some engine situations. Also, some later versions have electric feed back to the ECM

I would use a vacuum guage to properly determine when the vacuum is getting applied.
And yes you will need to go for a test drive with the guage connected.

As the others have stated, seeing little vacuum at idle isn't unusual. Since you have a check engine light I'm assuming you have at least an OBDI engine (depending on the manufacturer late 80's until-1996/1997) and a fault code should be stored in the microprocessor. The codes can be read on these with a jumper and then counting the number of times the light blinks. Google search OBDI codes with your engine manufacturer for more info. If you have newer OBDII engine (post 1997 vehicle), the codes can be read with a reader. In either case, your best bet to finding the cause for the light is to have the engine codes read. If you do not have access to a reader, many big chain auto parts stores (ie: Autozone, Pepboys, Advance Auto, etc) will read the codes for you at no charge with the hopes that you'll buy replacement parts from them. I'd start there to determine your next step. Good luck.

Lou
05 Travel Supreme Envoy

You said the "check engine light" came on. Did you use a scanner to see what the code was? If so what was the code? Post the code number and you will probably get some help. What makes you think the EGR valve is the problem?

the erg valve operates differently on newer vehicles… it used to be controlled by a port just above the idle setting.. so it received very little vacuum. so it was only part way open at idle. and full open upon decel. and any setting above idle it was open, unless under acceleration i.e. a low vacuum condition… to provide more performance.
on newer vehicles the egr valve is controlled by the engine control computer. using engine temp, throttle setting/position, vacuum pressure, inlet air pressure and temp. engine rpm, and altitude…
it is not un-usual to have the egr valve control hose to have little or no vacuum at idle.
the next generation egr will be total electric controlled. no vacuum line to the valve...

Moved from Forum Technical Support

Yes, no vac at idle.
You can disconnect the EGR valve vac hose and plug it off for a test drive. If the vehicle runs properly then you've found your problem. Keep in mind that some very new vehicles this will throw a code when you do this so be forewarned.

The vacuum doesn't get to a sufficient level until the engine is running at cruising speed so are you reving the engine up when checking the vacuum? The two checks I know of for an EGR valve are to let the engine idle and push up on the diaphragm inside of the valve. The engine should stumble. If you remove the vacuum hose first and then push up on the diaphram you should be able to prevent the diaphragm from returning by placing your finger on the vacuum tube. If it returns anyway the diaphragm is shot. You can do the second test with the engine off. If it fails either test, replace the valve.