This is my first time asking for help here so please bear with me.

As the title says, my 2002 Sentra XE bogs down when my try to accelerate hard. It's more noticeable from a stop, but seems to do something similar when I'm moving. I have the Mexican version as I live in Mexico and at high altitude (6,000 ft+). This problem started recently, after changing the power steering belt and fixing a leaking heater hose. When I tried to bleed the coolant system, a lot of coolant splashed out of the radiator and into the engine bay. I bought a cheap wifi OBD-II scanner to see if I could find some useful data. My short term and long term fuel trims are both -10% or lower. I checked the MAF data on the scanner, and it seems correct (6 grams/second at idle and rises when I hit the gas). However, I pulled off the MAF and the sensing wire inside is literally not there. How can it possibly give a reading and work without it? I disconnected the MAF and started the car, and I immediately got idle problems and the car went into limp mode. I checked the O2 voltage readings with the MAF disconnected and bank 1 upstream was maxed out at 0.94v, but bank 2 only reached 0.88v. Does this mean it is bad? I turned the car off and reconnected the MAF, started back up, and the idle was back to normal. I took it around the block and the acceleration problems were gone! This only lasted for a while though, and as the fuel trims went back to -10%, the acceleration problem returned. However, I noticed that one O2 sensor (upstream bank 2 again) was giving a normal fuel trim reading (around 0 to -2% vs. -10% on bank 1). I don't know what to make of any of this. Do I need a new MAF sensor? New O2 sensors? Or something else/all of the above? Any help is appreciated, sorry for the long post but I wanted to be as detailed as possible.

  • Does this have a split exhaust manifold for the two o2 sensors? I'd suggest doing a injector leak down test and swapping the two upstream sensors to see if the negative trim follows the sensors. Also 6 g/s @ idle is too high, the rule of thumb is maf g/s @ idle should be roughly the size of the engine. So I'd expect to see ~2.x g/s. You should consider doing a volumetric efficiency test as well. Can you provide pictures of the missing terminal on the MAF connector? If it's anything like the US models the QA+ terminal is used for the MAF signal. – Ben Jan 25 '18 at 23:06
  • Thanks for your reply. I will try to get to these points that you mentioned in the next few days if my schedule allows. The car has actually been driving a lot better now after disconnecting and reconnecting the MAF, but I'd like to know why. And yes, the exhaust manifold is split, 02 sensor 1 bank 2 is for cylinders 1 & 3 and bank 2 is for 2 & 4. The MAF connector is fine, but when I looked inside the MAF there was a filament/resistor that seemed to be missing compared to photos of that MAF I found online. I'll try to take photos and upload them soon. – Drew Jan 28 '18 at 3:28

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