I'm consistently getting code 5 (Exhaust gas recirculation faulty) on my 1995 E320 with 170k miles. I've read thru the archives and and 98% confident EGR working properly. I've checked the following:

- Applying vacuum to the EGR valve at idle cause the engine to stumble; I also replaced the EGR tube at 150k miles when replacing the head gasket

- EGR valve audibly snaps shut when vacuum is removed; it also has the white dot so I assume it has been replaced by the previous owner as a result of the TSB

- Applying 12v to the SOV also causes the engine to stumble at idle

- Air Pump and EGR valves are not reversed

- While driving, I monitored both the vaccum at the EGR valve and voltage to the SOV. EGR is activated with the engine warm around 1500 RPM and cuts out at idle and deceleration

- Wiring Harness has been replaced and is in good shape

The car runs fine. There are no codes on pin 8 or 14. Code 23 [Intake manifold pressure (in base module pressure sensor-) with engine running too
high/low] along with code 5 does appear on the builtin DM before the check engine light comes on; however, by the time the check engine light comes on code 23 is gone. Does this mean the EGR valve could be leaking?

What else can I look for? How does the HFM controller "know" that the EGR is not working? Thanks for any guidance.

__________________
as ever
Paul

1989 560SL
1987 300SDL
1987 300TD
1983 BMW 633CSi
1972 280SE 4.5