The DM checks the EGR during certain decel conditions. It looks for the high manifold vacuum (at the map sensor) caused by decel and then opens the EGR valve. If the EGR flow doesn't drop the manifold vacuum by a certain amount then it sets the EGR fault, even if the EGR is functioning. A partially plugged tube can cause this but when you have a pesky EGR code re-occuring then you not only have to look at the EGR function but also in how the DM monitors it.

__________________

90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff