'84 300D. I have noticed that the EGR area on the 603 engine needs to be cleaned of carbon. Does this hold true also on the 617 motors? When I blow air backwards into the switchover valve, it doesn't go through, and from what I understand it could be clogged. Can it be cleaned or do I need to replace it. The car has 202K miles, just replaced the rack bolt which smoothed out the rocking, but the idle seems more "rough" now. Will keep trying to adjust it. Also, HOW do you get the allen bolt on the steering box loose. This is a fairly new box, and the bolt will not move at all. Thanks for ANY ideas!

Robert
84 300D-T
76 Cad Fleetwood

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(.