Only when braking. It actually happens coming out of decel, when the ecu is looking at the potentiometer voltage to set the idle valve position. If potentiometer voltage drops below the lower threshold (somewhere around .4-.5V IIRC) it assumes a stalled engine and doesn't even try to catch and idle it.

When checking the potentiometer voltage, its this lower voltage range that must be smooth and linear. A glitch at 2V isn't going to cause this problem, but if it goes open somewhere around .5V-1V you've found your smoking gun

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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