# Help! Abrupt A/F sensor voltage spikes; Abrupt STFT spikes; Terrible Fuel Economy



## Bigplanz (Apr 10, 2009)

Look at freeze frame data for the conditions present when the code set. Let us know what they are.


----------



## TorJoe (Feb 29, 2020)

There is no data on the freeze frame page. The P0102 is always there as a "Permanent Code". And BlueDriver wouldn't let me clear it. 

There is one further wrinkle I can tell you about: as I said in my original, I have swapped out the MAF sensor that came with the car with another used MAF sensor. Prior to that, BlueDriver had been giving me two codes, P0102 and a pending code of P0113 (Intake Air Temperature Sensor 1 Circuit High Bank 1). After swapping the MAF sensor I am now left with P0102. P0113 has disappeared. But the lean spikes are still there.


----------



## Bigplanz (Apr 10, 2009)

TorJoe said:


> There is no data on the freeze frame page. The P0102 is always there as a "Permanent Code". And BlueDriver wouldn't let me clear it.
> 
> There is one further wrinkle I can tell you about: as I said in my original, I have swapped out the MAF sensor that came with the car with another used MAF sensor. Prior to that, BlueDriver had been giving me two codes, P0102 and a pending code of P0113 (Intake Air Temperature Sensor 1 Circuit High Bank 1). After swapping the MAF sensor I am now left with P0102. P0113 has disappeared. But the lean spikes are still there.


Not sure about Nissan, but many cars have the IAT sensor integrated with the MAF sensor. Spiking MAF can cause all sorts of odd behavior. Can you map the sensor along with TPS and RPM and log the trip? You can then find out out how the MAF correlates with he other two. Should be a smooth relationship, all three going up together, though not completely linear. My wife's Windstar kept cutting out at idle when pulling away from stop. MAF was all over the place. Would be steady, then plunge when the TPS and RPM went up suddenly. Worked normally when driving. Went to the salvage yard, got one for $20, and that fixed it. I know it is tough to wing a $100 new part at a problem, but my $20 wager paid off.


----------



## Brainbucket (Mar 30, 2015)

it almost sounds like there is a rip or crack in the air tube from the MAF to the throttle body. take it off and look at it closely. :vs_cool:


----------



## Bigplanz (Apr 10, 2009)

Brainbucket said:


> it almost sounds like there is a rip or crack in the air tube from the MAF to the throttle body. take it off and look at it closely. :vs_cool:


Good idea. Air tubes develop cracks that sometimes only open when the engine warms up. Now you see it, now you don't.


----------



## TorJoe (Feb 29, 2020)

I am very grateful for your comments and advice.

About a possible vacuum leak: I have read at multiple places online where they say that the effect of a vacuum leak is most pronounced when the car is at idle. But my Air/Fuel sensor voltage lean spikes seem to take place only when driving at higher speed. Does this mean the chance of a vacuum leak is low? 

By the way, I have posted a whole punch of charts here (MAF, RPM, A/F sensor voltage, post-cat O2 sensor voltage, catalytic temperature, timing advance for #1 cylinder etc) for those who has the interest to delve deeper. Please let me know if you see anything unusual in these charts that might explain my car's bad fuel economy.

https://forums.nicoclub.com/post6804180.html#p6804180

Thank you so much for your help!


----------

