Intermittent boost on a high mileage 2.5 is most likely bad throttle linkage microswitches. Located on the bracket that the throttle cable attaches to, the small grey microswitches tell the computer when the linkages are in the idle and full load positions. When they have a ton of miles the little roller followers that are part of the switches get flat spots and then don't actuate the switch. If the switch doesn't actuate, the computer still thinks its at idle and doesn't allow boost. Before you go modding everything give fixing the problem a try. Visually inspect the little rollers for flat spots and check the switches with an ohm meter.

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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