98 s14 with s13 ecu: Stumbly idle, smokes/rich, no rear o2 sensor....any ideas?

[Indolent]

98 s14 with s13 ecu (using enthalphy ecu conversion harness)
friends car's acting up and never wants to run right
-smokey/rich ... car revs up fine past 2500 rpms
-stumbly idle 700-400-700-400-700..

-s13 swapped ka24de block with s13 header/downpipe
-no EGR tube, all blocked off
-walbro 255lph fuel pump
-O2 / oxygen sensor (front) harness clip kinda melted
-Rear o2 / oxygen sensor is not hooked up, read it's "solely for diagnostics" but no check engine lights..on the s13 ecu.
-NO Check Engine Lights, but when i checked it was a MAF code 12 only, but i soldered it back up (cut from uninstalling SAFC), need to double check the wiring..and recheck to see if it's throwing the code again after i reseted the ecu

As far as the stumbly idle goes, would a bad MAF and an O2 / oxygen sensor cause this?

Anyone got any ideas? as always your help is appreciated

[bardabe]

mark the MAF and 02 sensor usually don;t cause a stumble Idle. sounds more like a bad IACV, or Vinh's harness is probably fucked up.also if you are using an S13 ECU, try using the S13 MAF unless it's tuned for some other MAF (wich I assume you are running right now)