1987 Toyota MR2 Car starts, but stalls, mostly when attempt

Recently, my 1987 toyota mr2 stalled while at a light and would not restart. After a brief period of rest, the car did start, however, it would stall when attempting to accelerate (i.E. – Rev motor and/or drive). This pattern continues with the period of time it will stay running and/or drive mostly varying. Prior to this issue, the car ran excellent, with the motor having been meticulously rebuilt from the crank up in 2005 (using genuine Toyota parts), including various engine compartment components – rebuild has approximately 71,000. Since then and the occurrence of the problem, thus far I have:

REPLACED:
* Fuel pump and fuel pump filter
* Fuel filter
* VSV (Vacuum Switching Valve, emissions)
* Plugs (Bosch Platinum Plus #4002)
* Coolant Temperature Sensor

RECENTLY REPLACED/SCHEDULED MAINTENANCE (prior to issue):
* Alternator
* Plug Wires
* Distributor Cap + Rotor
* Coolant Flush + Fill
* Thermostat
* Battery
* Air Filter
* Oil change (standard oil + filter)

BENCH TESTED:
* Air Flow Meter (PASS)
* EGR VMV (Vacuum Modulator Valve) (PASS)
* VSV (Vacuum Switching Valve, emissions)(FAIL, replaced)
* Coolant Temperature Switch (High Temp. Line Press. Up System) (PASS)
* Coolant Temperature Sensor (FAIL, replaced)
* Solenoid Resistor (PASS)
* Igniter (PASS)
* Ignition Coil (PASS)
* All relays in fuel, engine and coolant systems, including Circuit Opening Relay (PASS)

CODES:
* Code 4:
- replaced Coolant Temperature Sensor
Codes cleared following replacement; new code is Code 1 (Normal operation)

repairs and routine maintenance are performed using the guidelines and information in the Haynes Toyota MR2 1985-1987 Automotive Repair Manual (#92065 (1339)). I am an intermediate-level home mechanic with some prior experience in general automotive repair. That said, it is possible that my bench tests are flawed and/or I have not tested all possible culprit parts.

four notes: 1.) Another issue that began about 8-10 months ago is that the front radiator cooling fans (w/ A/C there are 2) run immediately after turning the key to the “ON" position. Attempts to correct have been fruitless; 2.) The car recently began to exhibit a very slight change in rev-down behavior. That is, after traveling on a freeway, when exiting to STOP the car would seem to want to stall but would not – the idle would simply appear slightly uneasy. 3.) Despite being in perfect time, a very, very slight miss does seem to be occurring below 900-RPM. This has been this way since the rebuild – no attempts to correct it appear to have any effect. 4.) The car is in need of a muffler (due to rot/holes in canister).

any idea where my problem lies? ECU is listed in previous Code 4 as possible culprit, but replacement of Coolant Temperature Sensor relieved this code. ECU is visually clean and unscathed.

thank you-
christopher