Need help with low fuel trims at idle (1 Viewer)

[jdavi67]

I am currently running rich (po172, po175) and I looked at my fuel trims to find answers. At idle both bank long term fuel trims trend to the 'high' negative teens (-19%), but under load and cruising they are within spec (around 0%). The LTFT trend very negative at idle or when I let off the accelerator to slow down. Where should I start to diagnose the root cause of this?

So far I have just cleaned the MAF sensor.

 

[SBANGLICO]

Check the FSM. It has diags for all DTC codes

 

[AVLTOYOTECH]

I am currently running rich (po172, po175) and I looked at my fuel trims to find answers. At idle both bank long term fuel trims trend to the 'high' negative teens (-19%), but under load and cruising they are within spec (around 0%). The LTFT trend very negative at idle or when I let off the accelerator to slow down. Where should I start to diagnose the root cause of this?

So far I have just cleaned the MAF sensor.

I am currently running rich (po172, po175) and I looked at my fuel trims to find answers. At idle both bank long term fuel trims trend to the 'high' negative teens (-19%), but under load and cruising they are within spec (around 0%). The LTFT trend very negative at idle or when I let off the accelerator to slow down. Where should I start to diagnose the root cause of this?

So far I have just cleaned the MAF sensor.

Have you checked for a clogged air filter or restriction in the intake ?

 

[jdavi67]

Have you checked for a clogged air filter or restriction in the intake ?

I checked it, and it's pretty dirty. Going to replace it and see what happens to my fuel trims. I graphed the MAF vs LTFT because there is an interesting correlation. Below MAF reading of 5lb/min, the LTFT is around -25%. However, above around 6 lb/min, the LTFT stays around -3% which is well within spec. Below is a graph depicting the relationship between LTFT and MAF.

 

[AVLTOYOTECH]

I checked it, and it's pretty dirty. Going to replace it and see what happens to my fuel trims. I graphed the MAF vs LTFT because there is an interesting correlation. Below MAF reading of 5lb/min, the LTFT is around -25%. However, above around 6 lb/min, the LTFT stays around -3% which is well within spec. Below is a graph depicting the relationship between LTFT and MAF.

View attachment 2506921

Is the flat MAF reading at the beginning of the graph at Idle?

 

[jdavi67]

Is the flat MAF reading at the beginning of the graph at Idle?

Yes it is. The other longer flat is part is also idling to get gas. I replaced the air filter and it didn’t not change those readings. My initial thoughts are the fuel pressure regulator since I’m seeing that wide swing which seems to hinge on vacuum. Or am I thinking of the MAF/LTFT graph relationship wrong?