I bought my 6MT G35 a year ago, and at first the throttle response was very quick and responsive. I have noticed a considerable decrease in throttle response over time after resetting the ECU/performing Air flow relearn procedure. I am at my wits end. I cleaned the MAF, performed a BG Fuel Induction Service, Installed a Stillen Hi Flow Intake, Installed a Stillen Cat Back Exhaust, Installed Kinetix High Flow Cats, and replaced one the O2 sensors on the catalytic converter. When I reset the ECU/Relearn Airflow the car runs perfect, BUT it loses throttle response as each day passes. Has anyone else run into this problem? I should also note that to confirm the loss in power outside of my butt dyno observation is the diminished sound of suction through the air filter and the loss of growl in the exhaust note that nearly disappears after a few days following the ECU/Air Learn. If anyone can help or has run into this exact problem please tell me what needs to be done. I am stumped.

 

I should also note that when i put the car into neutral while coasting I notice the drop in performance immediately thereafter. If I am coasting at a speed above 20 mph and put the car into neutral, the engine stalls. To me it seems as though the A/F ratio is perfect upon resetting the ECU/Air Flow Relearn, but then over a short time of driving thereafter begins to run too rich causing the sluggish throttle response.

 

It could be your MAF starting to flake on you, but that's a pretty uncommon failure on these cars.

 

I have been considering that as the problem, this is a $400 option that I can try to isolate and eliminate.

 

Sounds like you need to get tuned. The stock map is lazy

 

I intend to get osiris pro tune after i install Stillen Ceramic Headers, I will update if that works.

 

***FINALLY FIIXED*** The front wheel speed sensors were the source of my problem.

Since I have owned this vehicle, I have been chasing this AFR problem, where the engine has been running extremely rich, and not throwing any codes. I hope that anyone experiencing this issue gets the chance to read this.

I have replaced every sensor (some O2's twice) that I could find on the vehicle:
MAF, O2's front and rear, Coolant Temp, Cam Sensors, Crankshaft Sensor, etc

I have replaced my spark plugs 8 times in the last 2 years at least, replaced injectors, replaced coil packs, replaced air filter, replaced oil pan, replaced differential oil, replaced transmission oil,

Replaced Clutch, Replaced Flywheel, Replaced Wheel Hubs front and rear (bearing included) Cleaned every engine ground, Cleaned *almost all ground under dash*-still looking for 2 last ones

Basically, I have tried everything to correct this rich running condition with no CEL stored or active.

After 2 years of trying and failing, finally I received 3 stored codes:
C1108-Front LH Drivers Side ABS wheel speed sensor
C1109-Front RH Passengers side ABS wheel speed sensor
U1000-ABS grounding issue?

Coming full circle, I finally found out about the wheel speed sensors, which have a tremendous effect on my manual transmission(can only imagine how much they affect the AT models). Sure enough, I pop off the front tires, and the sensors are eyelet contact sensors, where the conductive portion of the contact was severely eroded and oxidized from road wear/moisture. FOUND THE PROBLEM and REPLACED with 2 new sensors,

car drives and sounds powerful again!!!!BUT ONLY INTERMITTENTLY, which I'm happy with, but I have my eye on the 2 rear wheel speed sensors located under the differential in the rear now, and the Vehicle speed sensor in that same area sticking out of the transmission.

I will update everyone with how this goes, in hopes that if someone has this same issue, they can have some light shed on what is a deal breaker for most in the same given circumstance.

Just to sum up, this journey has been hell, but I'm happy I have hope of a fix now that I'm finally at 100K miles after getting the car at 60k 4 years ago

 

I'm attaching a few logs of my ABS parameters and ECU parameters from cruises I've done over the past few days. The ECU ignition timing has my attention...