1992 240sx partial / full throttle sputter

[jxnkyle]

the vehicle description is a long one. here goes:

1992 240sx se, 128,xxx milesA/T swapped to manual1995 s14 kade and transmission, 137,xxx milesdual exhaust cams, intake redrilled +5*greddy shorty header, 3" header back, no catshort ram intake, relocated mafno scv (s14 intake)no egr

the problem is incredibly bizarre to me. the motor sputters on startup. idles 900 to 1200, sometimes constant, sometimes changing. gently cracking the throttle, it will rev up smoothly as high as i take it. if i open i a little wider and much quicker, it revs up but sputters badly. this is the same when driving. i can baby it and its fine. if i open the throttle too much it cuts out.

this is what i have done in attempt to fix/diagnose the problem in as close to chronological order as i can remember.

i replaced with known good parts from another running 1991 240:maf sensorecucoolant temp sensor (to ecu)throttle position sensordistributorignition coilfuel rail with injectors and fpr

none of these changed a thing, so i looked towards the harness. i shortened and re-pinned my maf sensor. no change. i ran a jumper wire from the maf ground wire (black) to a chassis ground. this fixed the problem at first, but the first time i put the pedal to the floor through 3rd and into 4th, it cut out again and my chassis grounded jumper had no effect connected or not. i then used the silver shrouding that wraps both the black and white wires as my maf ground and again ran good for one run into 4th gear before it went back to sputtering. i used another harness that had been cut in a few places, and cannibalized my own to make a new complete harness. once installed, the car ran exactly the same with no change. still sputters if quickly throttled, still cuts out if the throttle is opened too far.

sorry for the length, i'm trying to be thorough. any suggestions will be much appreciated.

[jxnkyle]

also the fuel filter has been replaced with a new one and the O2 sensor has been replace with a working used item. i have not tried the knock sensor, although when i unplug its subharness it does not change the way the motor runs. i also have not tried the fuel pump. i don't think this is an issue, because i can unplug the maf ground wire from the sensor and cause an extremely rich mixture, which makes it actually run decent above 5k rpm at wot. soooo...... feel free to be as confused as i am.

[Shift__BODOM]

Try checking the throttle position sensor. It could possibly be spiking during fast changes in throttle. The harness around that area is also very prone to rotting/shorting/generally getting fked up. Blew 4 fusible links until I checked the harness and realized a rotted wire was arcing to the valve cover

[jxnkyle]

i've replaced both the tps and entire wiring harness. no luck.

[jxnkyle]

no one else has experience with said symptoms?