Hi Steve. Thanks for the note.
Sounds like failure of the adjustable cam timing mechanism isn't a common problem... at least if you haven't seen it. :-)
Don't think the valve covers have ever been off this motor, so doubtful it was assembled wrong... and it runs flawlessly.
From what I can read, the test that the ECU does is once per "trip" and it confirms that the intake manifold pressure changes by more than a fixed amount within a second after the cams are ordered to advance. This apparently happens around 3K rpm or so depending on load/etc. If this happens twice, the code is set, but no check engine light is registered.
Guess I'll have to dig deeper and do the harness tests that the manual calls for. Meanwhile I've cleared the code; we'll see if it comes back.
As you said, it also calls for the solenoids to be activated one at a time to see if the idle turns rough... i.e. the cam adjusters are working.
Thanks again.

__________________
KenP

1996 S500 W140 Coupe