Cleaning MAF Sensor

Hi Andy,

I suggest leaving the MAF sensor alone unless you have a driveability problem. Use the plastic wand that comes with the throttle body cleaner so that you can direct the cleaner onto the throttle body plate (rotate open with your hand) and the throttle body interior.

Since the throttle body cleaner typically leaves an oily film (to lubricate the throttle moving parts), it is not clear that this is suitable for cleaning the MAF sensor.

 

I tried to post earlier, but the site went down

Anyhoo, here are factory shop manual prints of the throttle body and the MAF. The MAF is easy to remove, you unclick the connector, remove the two tiny philips head screws (Don't drop the screws), then wiggle out the MAF

 

GEE-zus what is wrong with the site? SLOOOWWWWWW

This is a photo of the MAF before cleaning. I couldn't get a clear photo of the hot wire guts, but the bulb thing is the temp sensor. I theorize that layer of ash is the oily residue from the PCV system. Both my Prius and my FJ have it

 

The MAF after cleaning. A big difference. The ash-like stuff was also coating the two hot wires inside the MAF. It only took a couple of spritz applications to the RTD bulb, and the MAF wires, to get them squeaky clean

 

Here is the only clear photo I have of the MAF guts, after cleaning. Obviously, somebody with a better camera will be able to get better photos. You can see the ash deposit is gone and the two hot wires are squeaky clean

When I cleaned the Prius last fall, there was perhaps a teeny bit of difference in how it ran. With the FJ, a much more noticeable difference

 

For reference, looking straight down at the Prius airbox, with the lid removed. You can see the MAF and below, the closed throttle plate

 

It would be best to remove the MAF before cleaning the TB, to avoid TB cleaner residue on the MAF hotwires. With the MAF removed, use one hand to open the throttle shaft at the return spring

Be gentle opening the blade, as the TB is electric drive, same as on my FJ. With the blade fully open, use a few gentle sprays from the TB cleaner. More is *not* better! Get too much cleaner into the intake, you could have a no-start, or a very poor start

Eg: when I cleaned the TB on my FJ last fall, it clearly needed it, along with the MAF. There is no external return spring on the FJ throttle body, so I had a neighbor kid sit in the driver seat, with the motor off and ign On, keeping the gas pedal floored. You can NOT use this procedure with a Prius, once you power on and floor the gas pedal, the gas engine will try to start

While the little bugger kept the pedal floored, I used the TB cleaner to spray off the heavy buildup from the blade and passages inside. I'm pretty sure I used to much cleaner, as once I had everything together, it was hard to start and ran roughly for a few minutes

However, once it settled down, and I went on the highway to blow everything out, there was a very immediate and apparent difference in how my FJ ran

Note, if the MAF has never been removed before, the o-ring might stick. Gently wiggle it out, don't use a tool to try to pry it off.

 

I am leaving tomorrow morning on a business trip, will be gone about a week. Any questions will have to wait until then

 

Physically removing the throttle assembly is not difficult and will allow you to do a much better job cleaning. You will have to block to coolant lines. Bolts (5/16" I think?) wrapped with some vinyl tape make good plugs for those. You will unplug the MAF and throttle motor electric plugs.

When the whole thing is out you can decide to sab the MAF or leave it alone.

Check out the goo in the PCV lines also - it may be more than you expect to find.

 

This is such good info!
It is winter up here now with temps in the teens. I'm getting only about 36mpg. I have replaced my battery with an Optima, have 42/40 psi in my Michelin harmony tires. I have blocked the top fins of my hood. I am trying to drive doing the P & G, etc.

In the summer I'm only getting about 44 mpg. I'm no mechanic, and it bugs me that it may be some little thing. I'm almost wondering if this elusive 50 mpg is in the same category as Santa Claus and the Easter Bunny..........

I will now try this.......I suppose it could be worse, I could have those HID headlights....

Frank D.

 

Thank you jayman for the photos. I went from being scared to touch the MAF sensor to a DIY in one day - today.

I cleaned the MAF sensor with CRC MAF sensor cleaner from AutoZone. Also got a throttle body cleaner there as well as gas tank fuel injector cleaner. Cleaned the throttle body using these instructions(thanks Bob Wilson):
Cleaning Prius Throttle

Went from engine shudders and shutdown 10 seconds after starting, with red triangle/engine check lights etc., to a great sounding running engine and no lights on my 2002 Prius with 96K miles. I had only previously changed the plugs on this car once, with everything working great until this week. Cleaning the MAF sensor and throttle body seems to have done the trick. I plan on doing the same to our 2004 Prius with 103K miles next week.

Had previously got this quote from dealer(but had put it off):
EFI and t-body (includes both Fuel Injector Cleaning and Throttle Plate Cleaning) $184.95
Clean MAF Sensor $64.95

I was going to pay $185 + $65 = $250 then x 2 for our 2004 Prius = $500.

Supplies cost about $25 for both cars (not including engine air filters)
My savings $475
I am SOOOOOO thrilled.

Thank you soooo much PriusChat.

 

My 2004 has 111K miles and I decided to remove and clean the MAF sensor. I first removed the air cleaner housing, then removed the MAF sensor from the housing.

The temp sensing bulb had an amber color so it was not particularly dirty. The two sensor wires hiding inside the sensor looked OK. Regardless, I used the CRC MAF sensor cleaner, spraying off the bulb and the two wires. I also used the cleaner to get rid of the dirt and dust on the sensor body near the wiring harness connector.

I cleaned the throttle plate and throttle body interior, using three Q-tips dipped in rubbing alcohol. Some black gunk buildup but not bad. I had previously cleaned this at ~60K miles.

No obvious change in driveability, after putting everything back together.

 

With my '04 Prius, never had any huge difference in driveability before/after. The "puddle" at the bottom of the intake is common for that vintage Prius.

My '07 FJ is entirely different. If I don't clean the MAF every fall and spring, even the auto trans begins to shift weird.

When I was at the CTIA convention in Vegas, back in March, I had the chance to hook up with old buddies, and a couple have FJ's - one in Vegas one in St George. Not exactly bitter cold climates

The buddy in St G, his '07 FJ already has 45,000 miles on it. He follows my exploits on the FJ forum, and wanted me to clean his TB and MAF, along with changing the plugs, the gear oil, naturally I had to "work" for a "free" stay and meals at his house!

His TB was spotless, so was the MAF.

WHich is why I'm now convinced - unless somebody can offer another plausible explanation - that short trip operation in temps down to -40 dump a lot of oily vapour into the intake, which coats the MAF and TB.

A vehicle operated in such conditions, say Winnipeg or Thompson, CHurchill, Lethbridge, Whitehorse, Ft Greely, etc will be expected to have deposits on the TB and MAF. My 2000 GMC Sierra always had heavy deposits in the TB and Idle Air Control passages, colleagues with similar vintage Chevy trucks in the SW United States did not. The MAF was ok because it was quite far upstream from the TB

 

I realize that many posters have noticed this puddle. I personally have not seen this with any of the three Prius that I have owned. The intake manifold floor is "damp" but there is no "puddle".

Your hypothesis regarding short trip operation in extremely cold weather is quite reasonable.

 

I suppose an engine block heater would help reduce the issue with the cold weather?

 

A block heater helps with starting and with faster warmup. It will not do anything to minimize condensation in the oil

Just the opposite is what I have noticed. With equipment parked outside, and powerful coolant and/or oil pan heaters, they actually CREATE a lot of condensation in the motor block.