Can't get A/F ratio Stoich
 

Hey guys I've posted about this problem before but now I would like to throw out one final attempt at solving my issue. So I have a 1999 Max which I did a 2001 De-K full motor swap on. Everything on the motor is stock expect the following: Cold air intake, adjustable fuel pressure regulator with gauge set at 3bar, 00VI block off plate and butterfly removed, currently no IAVC, but I have a 4th gen IACV and adapter that I have used in the past (with same issue w/o using IACV), 2.5 full exhaust except stock headers. Original wire harness from 99, and using a 96 manual JWT ecu that I ordered for this specific build. I also have the stock ecu and a 98 manual ecu. Car started as auto, I swapped to 5 speed. Car runs the same off all 3 ecu's. The issue is that when I start the car, it will primarily run very lean, occasionally it will start up very rich, as according to my wideband 02 sensor and I can smell the difference in rich and lean conditions. The car will idle forever and sometimes bog a bit and then come back up, but once I begin to drive the car it will run lean and blank off the wideband and when I slow down or let off/stop the car wants to stall and will. Sometimes it will start up rich, and drive very rich also and you can feel the sluggishness. I have replaced the MAF, and tested the wires, all checked good. My mechanics OBDII reader showed the ecu pulling gas for an unknown reason. He suggested changing the MAF and I did with no difference. If you can think of any ideas please let me know and ask me any other questions you want to know more about.
Thanks

Hmm puzzling as I kinda have same problem. I ended up changing my sparkplugs injectors and bought six oem coilpacks and it solved the random stalling, but smetimes it'll start either lean or rich.. try getting new coilpax? cam crank pos senser?

Sounds like you need an AFC or better. What are the actual ratios when you say lean and rich?

Mine goes off scale lean when I let off, but doesn't die. (>21 AFR). Always starts up rich, as it's designed to (10.9-11.2, 0% correction via AFC, after warming up, perfect 14.7, 0%). Runs fine part throttle cruising (14.5-15.1, +5-7%). Get on it and it's in the high 12's +14-16%. I've got an AFC with 560cc's and a 4" intake. Never thought it would run this well with this set-up.