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Missing and running very rich Need Ideas

Hi all. Having a problem with 685/2000. Started a few months ago, would miss at idle and clear up as rpm increased. However one day it started to do it all the time and make huge quantities of black smoke. Checked codes and replaced:

coolant temp sensor
O2 sensor
had injectors cleaned and flow tested
replaced spark plugs
wires
Fuel Pressure is 35psi
Cam and Ignition timing is right on
drained gas tank and refilled
Checked for IC Hose leaks-none found
EGR block off plate

Started checking AFM, was reading 60-70 Hz, FSM says at idle should be 20-50. Got a used AFM, same thing, got another one, and again same thing.

Now, if i take the brake booster hose off the intake, it clears up a lot, but runs at 2500 Rpm, which tells me as im introducing more un-metered air, it is making the AFR's closer to where they should be. but why is it reading so high? I even made an adapter to mount the AFM right to the throttle body, and that did nothing. ECU was repaired several years ago for leaking caps, but also the ISC took out the drivers, but has run for several years like that.

Ideas?
 
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