Diagnosing issues in your Nissan 350z often starts with connecting an OBDII scanner to read diagnostic trouble codes. However, what if you can’t even establish a connection? This was the initial hurdle faced when troubleshooting a throttle cut issue on a 350z. The first step to any modern car repair, especially when dealing with engine performance problems, is accessing the car’s computer via the OBDII port. In this case, no power to the OBDII port meant no communication, and no diagnostic data to begin with.
The solution, thankfully, was straightforward. Acting on expert advice, the culprit was traced to a blown fuse – specifically fuse number 34 located within the relay box in front of the battery. Visually, the fuse appeared intact, highlighting the importance of using a multimeter for accurate diagnosis. A simple resistance check revealed the fuse was indeed faulty. Replacing this fuse restored power to pin 16 of the OBDII port, bringing the diagnostic system back online.
With OBDII access restored, the ECU’s learning was reset, and NATS (Nissan Anti-Theft System) codes were cleared. The engine now started, a significant step forward. However, the original problem – a cut throttle – persisted. While the engine revved smoothly with gentle throttle input, applying anything beyond 50% throttle resulted in engine bogging and a sensation of fuel or spark cut.
To understand this further, data logs were recorded, capturing key engine parameters: RPM (Revolutions Per Minute), AFM (Air Flow Meter) Volts, Accelerator Pedal Volts, and Throttle Position Sensor (TPS) readings. The data revealed a clear correlation: as the TPS sensors indicated full throttle (reaching 4V+), the RPMs inexplicably dropped, only recovering to around 1200 RPM when the throttle was released.
Time, RPM, Air Flow V, Accel P1, TPS 1
000.078, 962, 1.38, 0.78, 0.66
000.156, 950, 1.38, 0.78, 0.66
000.203, 950, 1.38, 0.78, 0.66
000.265, 950, 1.38, 0.78, 0.66
000.328, 962, 1.38, 0.78, 0.66
000.406, 962, 1.38, 0.78, 0.66
000.468, 962, 1.38, 0.78, 0.66
000.531, 962, 1.38, 0.78, 0.66
000.593, 962, 1.38, 0.78, 0.66
000.687, 950, 1.39, 0.78, 0.66
000.750, 950, 1.39, 0.79, 0.66
000.828, 950, 1.38, 0.78, 0.66
000.875, 950, 1.38, 0.78, 0.66
000.953, 950, 1.38, 0.79, 0.66
001.062, 950, 1.4, 1.84, 0.67
001.187, 862, 2.92, 4.6, 4.13
001.265, 775, 2.35, 4.6, 4.13
001.343, 700, 1.94, 4.6, 4.12
001.421, 775, 2.62, 4.6, 4.12
001.500, 738, 2.98, 4.6, 4.12
001.593, 650, 2.18, 4.6, 4.12
001.687, 750, 2.27, 4.6, 4.13
001.750, 688, 2.3, 4.6, 4.12
001.828, 638, 2.41, 4.6, 4.13
001.890, 600, 1.82, 4.6, 4.12
001.968, 538, 1.79, 4.6, 4.12
002.062, 675, 2.56, 4.6, 4.12
002.140, 650, 2.46, 4.6, 4.12
002.250, 700, 2.68, 4.6, 4.12
002.328, 638, 1.91, 4.6, 4.12
002.390, 662, 1.95, 4.6, 4.13
002.484, 662, 2.46, 4.6, 4.12
002.562, 588, 1.8, 4.6, 4.12
002.640, 638, 2.34, 4.6, 4.13
002.703, 700, 2.67, 4.6, 4.13
002.765, 662, 2.09, 4.6, 4.13
002.875, 725, 1.94, 4.6, 4.12
002.984, 700, 2.52, 3.52, 4.06
003.078, 875, 1.62, 0.78, 0.88
003.171, 1125, 1.4, 0.78, 0.69
003.265, 1212, 1.48, 0.78, 0.69
003.359, 1188, 1.5, 0.78, 0.69
003.437, 1200, 1.52, 0.78, 0.69
003.546, 1262, 1.51, 0.78, 0.68
003.609, 1250, 1.52, 0.78, 0.68
003.703, 1262, 1.48, 0.78, 0.68
003.765, 1262, 1.5, 0.78, 0.68
003.859, 1275, 1.5, 0.78, 0.68This data pointed towards a potential issue with the Mass Air Flow (MAF) sensor. Earlier, a P0113 code (“Intake Air Temperature Circuit High Input”) had been observed, further suggesting MAF sensor problems. It’s hypothesized that aggressive cleaning of the MAF sensor with contact cleaner might have damaged its delicate heated wires, especially if the sensor was warm at the time of cleaning.
A faulty MAF sensor can lead to a lean running condition, particularly at wide open throttle when the fuel system enters open-loop mode for maximum power. With an under-reporting MAF, the engine may not receive enough fuel, causing it to bog down and potentially misfire at higher RPMs. Crucially, this lean condition might not trigger a check engine light or any diagnostic codes because it occurs in open-loop operation, where the ECU relies more on pre-programmed maps than sensor feedback. This perfectly aligns with the observed symptoms: no CEL or codes, yet significant throttle cut and performance issues.
While the Body Control Module (BCM) is mentioned in relation to the NATS issue, in this specific scenario, the focus shifted to the MAF sensor as the primary suspect for the throttle cut problem after resolving the OBDII port power issue with the fuse replacement. Further investigation should include checking fuel trims and O2 sensor readings to confirm the lean running condition and pinpoint the MAF sensor as the root cause of the 350z’s throttle cut.
