[Vwdiesel] 02 TDI, faint tapping when under load

[Stephen Sherman]

Thanks for the replies.

Answers to questions (and ask a few of my own)

There are 109K miles on the engine.  Seems to be very well maintained. 
PO did regular oil changes and the like.

Possibly valve lifters (though of that), but when I probed around the 
valve cover with the stethoscope, didn't hear anything that sounded like 
a tapping.  And I would assume that a lifter would be noisy at all rpms 
and especially low rpms, with and without load. Doesn't explain the 
tapping going away when you lift the foot of the go pedal at high rpm 
(2k or so).

I can't say for sure if the tapping frequency is in sync with engine 
rpms.  It wasn't conclusive to me (but then again I have lousy musical 
pitch too). It does seem to vary some with RPM or load, but not entirely 
in sync.  If it was part of the engine mechanics it should be exactly in 
sync with the rpms I would think.  It might be, but I wouldn't swear to it.

Either the ERG or Turbo control valves sound like a good thing to check 
out. I suspect the Turbo one, as it comes on with engine load and IIRC 
the ERG is not really doing much at load. Might explain both the load 
connection and the mystery location (engine vs dash) since that valve is 
right on the firewall.  Now just have to figure out how to check it.