PSA – Always Clean Your MAF Sensor

It’s always the little things that get you.

You would think that in the seven years of ownership of Project Rough, my 1999 ER34 Nissan Skyline GT-T, I would have figured this out by now.

Yes, this is the same Project Rough from Speedhunters – Just so we are all clear on that. I was amazed how many people didn’t know that I was the Ron Celestine from Speedhunters, but then again, I had virtually stopped working on Tokyo Tuner, so I shouldn’t be that surprised, I guess.

Anyways – Project Rough had been acting Rough (surprise surprise) a few months back before getting it ready for its Shaken inspection. 

I’ll put together a 2025 version of my “How Modified Cars Pass Shaken In Japan” series that I created back in 2019 for Speedhunters.

Rough was running like crap, and the telltale signs of a bad 02 sensor were present. Black smoke puffs out of the Kakimoto Racing x R31 House exhaust. Exhaust fumes that would make the devil blush.

An abnormal amount of black soot builds up on the tip, and the occasional soot that shoots out and stains the driveway.

When the 02 sensor starts to go out, the ECU struggles to calculate the proper fuel-to-air ratio, and in the case of Project Rough, it injected more fuel for the combustion, thus causing the mixture to become rich.

Since my car wasn’t shaken, I couldn’t drive it around to see how it affected the performance, but the fact that even at idle, it was running poorly, I was confident this was the solution.

Spoiler Alert – that wasn’t the only thing wrong, but future Ron would discover that.

I changed out the old O2 sensor with a brand new one, and the earlier-mentioned symptoms went away. Satisfied, I finished the rest of the shaken preparations and got it back on the road.

Since I hadn’t driven Rough in over a year, some of the other symptoms that were present I didn’t notice.

The rpm at idle was higher than normal, but I thought that was due to the smaller GT2525 turbocharger we installed without retuning it.

Then there was the “choppy” 1st gear. Whenever I would leave the car in 1st gear, it would jerk and buck if I drove at part throttle. If you drove it up to 3,000 rpm and shifted into second, nothing happened. So, I thought this was the 1.5LSD diff doing.

Then, things started to get obviously worse almost all at once. It felt like it was significantly down on power; it refused to rev over 4,000 rpm, and the rev idling got so sporadic that it felt like it was trying to stall at traffic lights.

I began to think the problem lay with my brand new 02 sensor. Perhaps I was unlucky and had received a faulty unit. Knowing my luck, that wouldn’t surprise me.

Then, it dawned on me. Not once since I’ve owned Project Rough have I ever cleaned the Mass Air Flow sensor! But, there’s no way that a little sensor in the air intake could cause that much chaos. Could it?

Just like the 02 sensor, the Mass Air Flow Sensor (MAF) calculates how much air is being sucked into the system. The ECU calculates this value and, with the 02 sensor, computes the proper air-to-fuel mixture. 

Unbeknownst to me, the MAF sensor is incredibly sensitive and even build-up can cause the sensor to misread the situation. I was doubtful that a simple cleaning could be my savior, but seeing that the sensor hasn’t been cleaned in at least seven years, I figured I should start there.

Being a man of science, I wanted to gather before and after data to see if I could put a numerical value on any changes that occur. With the Apexi FC Commander, I could monitor several values of interest, in particular the injection duty, engine timing, air flow, and engine revs.

These are values that I pulled a few minutes after letting the engine warm up.

The injection duty and engine timing seemed pretty high to me, but I’ve honestly never looked at these values before, so I had no frame of reference on what is good or not for my RB25. What you also can’t see in this image is the rpm hunting around from mid-700s to high-900s. 

With my baseline established, it was time to clean the sensor. Depending on your air intake system, getting access to the MAF sensor can be easy or a pain in the ass. For Rough, it was as simple as removing the Apexi Air cleaner and disconnecting the tube assembly from the rest of the intake. 

As this is an incredibly sensitive device, you really shouldn’t try to clean the sensor in a diy style. No soap and water, or any of the typical nonsense I would try.

This is one of those right tools for the job moments. These types of cleaners flash off fairly quickly and won’t leave residue or “hard water” spots that can throw off your sensor. 

Unplug the sensor and or disconnect the car battery. Aim the nozzle 10 to 20 cm away (follow the instructions on whatever product you have) and go ham. 

It should flash off fairly quickly, but give it five to ten minutes just to ensure everything is dry. Reconnect everything, and that’s it. 

There was an awful amount of oil in the intake. I’m not sure if it developed blow-by from everything running rough, or indicative of something more serious developing. I’ll keep an eye on it and the oil levels.

Since I was already here, I cleaned the air filter cone as it too hasn’t been cleaned in years. 

Fingers crossed, I turned the key and fired the RB25 to life. Instantly, I knew cleaning made a huge impact. The way it fired up sounded smooth and crisp. The idling hunting stopped. A few blips of the throttle filled the neighborhood with clean, quick succession roars.

The values on FC Commander were already lower at a cold start than they were before cleaning with the engine already warmed up. 

 Once the engine was warmed, I pulled these values off the controller.

To say I was flabbergasted would be an understatement. This really worked!

The test drive all but confirmed the data and subjective observations I had at my house. Rough felt like it had an extra 50 or so bhp. Incredibly responsive. Revved cleanly throughout the entire rev range. 

And for the first time in I can ever remember, the car stopped bucking and jerking in 1st gear part throttle applications.

At this point, I felt rather dumb. They say you should clean your MAF sensor every oil change, and they are absolutely right. 

Learn from my mistakes. Find 30 minutes out of your day to clean your MAF sensor. If you are like me and can’t remember the last time that it was ever cleaned, you might be surprised how much performance is being left on the table.

Oh, an added bonus has been better fuel economy as well. My cluster is slightly broken, so I can’t report a % of improvement, but I have been able to do my daily route more days than I could before the cleaning.

TLDR – Clean your damn MAF sensor with a purposely designed cleaning spray.