The EGR on 84 us model 617 does not use a switchover valve. It is temp and throttle position that regulate the vac to EGR.
The switchover valve on the firewall is for the boost enrichment, aneroid compensator.
It should flow air fom the line from intake to the line to inj pump when de energised. when energised it dumps air from intake line to atmosphere.
the line has along banjo bolt at the intake which is often full of crud. reomve and clean .remove line from inj pump.then blow through line to blast out the carbon thats in the valve and line. if valve is plugged, replace.
Niether will have any effect on idle quality though 8(.