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99 Nissan Altima
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Discussion Starter #1
I have a 99 Nissan Altima with a 5spd and I have had an issue where if I barely press on the gas pedal it will sputter for a second and then level out once I give it more gas. So I unplugged the IAT sensor, (I don't remember why exactly) forgot to plug it back in and my car ran great, just like when I started it for the first time after the engine rebuild. So I replaced the sensor, plugged it in and......the sputtering returned. So I unplugged it again and it runs great like before. I know this isn't exactly good so would anyone have any ideas on what could be causing this? My only idea at this point is to check the wiring but the more ideas the better.
 

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I have a 99 Nissan Altima with a 5spd and I have had an issue where if I barely press on the gas pedal it will sputter for a second and then level out once I give it more gas. So I unplugged the IAT sensor, (I don't remember why exactly) forgot to plug it back in and my car ran great, just like when I started it for the first time after the engine rebuild. So I replaced the sensor, plugged it in and......the sputtering returned. So I unplugged it again and it runs great like before. I know this isn't exactly good so would anyone have any ideas on what could be causing this? My only idea at this point is to check the wiring but the more ideas the better.
There could be another problem. With the IAT unplugged, the ECU might have switched to "fail safe" mode giving the appearance of smooth running.

Is the MIL lighting up? You might want to perform an ECU code readout with a portable scan tool to see if any fault codes are set. The tool can be purchased at most auto parts stores or online at Amazon.com. Post the actual codes here on the forum so that we may be able to help you further. If there is one or more fault codes set, they can help point to the malfunction.
 

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I'm going to assume the original poster has the same issue as I, code p0111, and same as him I also replaced the iat with a brand new one, plugging in new iat causes rough idle, poor acceleration, vehicle luchring, and makes vehicle almost undrivable, the prongs on my iat were touching and sensor was shorted when I pulled it so idk if that can kill the pcm, I've also hered a clogged cat can cause a backfire into the intake causing the iat to read false higher temps but I don't think that's the problem because it runs the same cold as it does warm, I assume the original poster is having the same problem, I have not checked pcm yet nor know how to
 

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99 Nissan Altima
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Discussion Starter #5
The only code I'm getting is p1336 which is for the crank sensor that I already replaced (twice). After doing some digging I believe I may have a broken tooth or two on the flywheel. If I remember correctly the crank sensor works with the Iat and Map sensor when the motor is at operating temperature ( closed loop) and if there is something wrong with the flywheel teeth it can mess with the idle and driving and such. I literally replaced everything but that and I don't have a vacuum leak either. Also it starts pretty rough and I've heard it grind here and there. I will be trying that next and will post back whether it fixes the problem or not. Might be a bit because it's going to be hot as shit these next two weeks.
 

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The only code I'm getting is p1336 which is for the crank sensor that I already replaced (twice). After doing some digging I believe I may have a broken tooth or two on the flywheel. If I remember correctly the crank sensor works with the Iat and Map sensor when the motor is at operating temperature ( closed loop) and if there is something wrong with the flywheel teeth it can mess with the idle and driving and such. I literally replaced everything but that and I don't have a vacuum leak either. Also it starts pretty rough and I've heard it grind here and there. I will be trying that next and will post back whether it fixes the problem or not. Might be a bit because it's going to be hot as shit these next two weeks.
The crankshaft sensor on the Altima KA24DE engines prior to 2002 is used only during diagnostic testing; it has no effect during normal operation. So the P1336 fault is a non-issue to your problem.
 

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Discussion Starter #7
Well then I guess I'm running it into the ground because I'm out of ideas at this point hahaha. thanks though
 

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With the IAT unplugged, the ECU switches to "fail safe" mode giving the appearance of smooth running. The ECU will just assume the intake air temperature is 68°F. This is called a fail-safe mode. The ECU will still use all the other sensor data. Even if the actual intake air temperature is much different than 68°F the ECU will still adjust air-fuel ratio using the O2 sensor feedback.

The O2 sensor may be causing the problem. The easiest way to check the O2 sensor is to view the live data with a scan tool and check that the voltage output is correct.
 

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After checking for vaccume leaks, I am down to tps or ECU/pcm one of the two is causing the problem but if tps is bad the vehicle shouldn't run with iat unplugged, double check yours to be safe, my car wouldn't run good with new iat plugged in yesterday, now it does and runs great, so I'm leaning towards a pcm issue, hope this helps, will update when new pcm arrives
 
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