Vehicle information:
1995 E320 Sedan
101,000 miles
updated wire harness
new head gasket 8K miles ago
rewired throttle actuator
new motor mounts 5K miles ago
recent plugs (F8DC4) 7K miles ago
new coil to plug connector boots 5K miles ago

Symptom:
Slight intermittent engine burble or hiccup when at idle after engine has reached operating temperature. Hiccups/burbles are random, average time between is 5 to10 seconds. Symptom seems most pronounced when coolant temperature is in excess of 90C. No codes present in DM, HFM/SFI, or EA modules. Engine performs perfectly under all other operating conditions.

What I have tried so far:
Swapped coils, plug boots, and wires with known good from other vehicle, no change.
Removed spark plugs, check for fouling—none found. Replaced with new set of F8DC4 plugs—no change
Removed EGR valve, checked and verified complete valve closure and freedom of movement. Reinstalled—no change. Tried one bottle of Techron in case of dirty injector(s)—no change. Look for obvious vacuum/air intake path leaks—none found.

Anybody have suggestions on what I might try or look for?

J. M. van Swaay