Still running rough

[Roa, Greg]

Well, I have a few more developments.
Car is a 87' 5kcstq with MC-1, Mac 11-c.

Replaced the coil last night and did some fuel pressure testing on the car.

Fuel pressure tests (static and control) are dead on for the car according to the bentley specs.

Car starts great, idles great until it is warmed up.  At that point, I get a random misfire at idle, and low engine speeds.  If I pull the o2 sensor connection, I get a nice smooth perfectly steady idle.  With O2 sensor disconnected, I get a frequency valve duty cycle of 49.5% and a o2 sensor reading that fluctuates between .875v and .885v

When I reconnect the o2 sensor, my frequency valve duty cycle drops, and fluctuates between 24% and 38%.  During this time, my o2 sensor readings swing wildly between a few milliamps and 1v, with the car misfiring as before.

Car has had o2 sensor, injectors, injector o-rings, fuel metering head, coil, plugs, wires, rotor, dist cap, ECU, misc vacuum lines, michelin man hose, idle/wot switch replaced in an effort to cure this problem.

I checked and cleaned the grounds, and clamped off vacuum hoses in an effort to eliminate the rear main seal, decel valve, and crankcase breather hose.

I have not checked the MFTS, but the dash gauge works fine (don't think this would cause anything of the sort- should just limit boost, right?).

Anything else to suggest?  Is there a way to test ecu's wiring to it's temp sensor (the one by the power steering pump bracket)?  Something is keeping the engine from running properly in closed loop, but I can't find it.

Thanks!

Greg Roa
Cincinnati, OH
86' 4kcsq x2
87' 5kcstq
93' 90CS
83' 944