At times it will down to -7% to -4% and then rises again to -12% ~ -14% after the car getting warmed up for longer time. The problem seems to be very elusive and not sure what could have caused such weird behavior of the long-term fuel trim.
There is one of the most obvious signs to this problem when stepping on the gas pedal briefly the long term will go down between 0.0 to -7% which is very good and that indicates the car is lacking air for combustions.
So, the presumptions analysis goes like this - At cold start the car run extremely rich around -32% to -34% and it goes down to -7% to -4% at optimum temperature @ 83 ~85 degree Celsius. As the car being driven and warmed up longer the fuel becoming thinner and capable to deliver more / faster but lack of air and the long-term fuel trim starting to go up around -12% to -14% again and sometimes -25% when running at idle or cruising without stepping on the gas pedal. However, when stepping on the gas pedal briefly the long-term fuel trim goes down between 0 to -7%. This concludes to a presumption that the car is lack of air flow when idle or cruising without stepping on the gas. But the real problem is what could have caused the lack of air?
These are few things tweaks that has been performed but no changes so far
| Checking Parameters | Fuel Trim Improvement |
|---|---|
| Adding magnetic fuel saver | It seems to work for a couple of days but after that the fuel trim running rich again -32% maximum which is worst. This concludes that magnet have little effect to the fuel combustions |
| Torque Spark Plugs @ 17Nm | Nothing changes |
| Changed / clean fuel injectors | Not yet |
| Clean catalytic converter | Not yet |
| Clean Throttle body (ISC and TPS sensor) | Not yet |
| Replace air filter | Not yet |
| Replace pcv valve | Not yet |
| Replaced Oxygen Sensor ( O2 sensor ) | No Improvement |
| Replace Map Sensor | Not yet |
| Replaced fuel pump | No improvement |
