Mazda 3 2010 1.6i - Negative fuel trims

[djkoss86]

Hi to all!

Due to some drivability issues I've decided to verify/diagnose my Mazda 3 1.6 petrol engine management. Car has 54.000 km, spark plugs, air filter, oil were changed recently, no cell.

With the help of a diagnose tool, I've managed to read the Long/Short fuel trims and air/fuel ratio values. So, I've discovered that:

- Long fuel trims were -35%
- Short fuel trims were -28%
- air fuel/ratio was 0.96 (at idle).

Therefore, I'm guessing that my Mazda's engine runs rich, due to the negative values of the fuel trims (ECU is subtracting fuel).

What can be the causes of such negative values ?

I have a video showing RPM behavior which in my opinion is not normal: https://www.youtube.com/watch?v=DSZCR1pvWfU

This started just after I cleaned the throttle body (which is DBW).

Any thoughts of why it does that pause at 1200 rpm then goes up 50-100 rpm and then back to normal ?

[Booter22]

do you have defrost or ac on? I mean its a hard question to answer we don't have this motor in our 3s but in the mazda 2. so it could be set up a tad different. maybe after the TB clean you should reset the idle position to 0 try a battery pull and let it sit for 10 minutes then put it back on and let it run and idle for 10 minutes do not rev it. see if that helps.

[djkoss86]

Nope. Defrost and A/C are off when it does that rpm jump. I did reset the ECU, also recalibrate TB at the Mazda dealer through Mazda scan tool. Still no luck.

I think that kind of behaviour is has something to do with those negative fuel trims values. Or maybe a faulty MAF ?

[Booter22]

is the maf dirty? maybe not getting a good reading?

[TheMAN]

probably a vacuum leak... was the throttle gasket ever replaced?

[djkoss86]

The throttle body gasket was not replaced. I have order it from Mazda last week. It takes some time to arrive. MAF sensor is clean also the IAT.