MAF and Throttle body cleaning

Notamech · April 24

So yesterday I started my car drove on to the road and immediately got stuck in traffic. Given the engine was cold it was running as the car was trying to warm up. While sat in traffic I noticed something strange, at idle I could feel vibrations of the running engine in the cabin intermittently. The best way to describe it would be as if the car is running lean and was close to cutting out except it wouldn't cut out. when the car is moving its fine. Which got me thinking that given it has run 94k now perhaps as good practice it might be worth cleaning the MAF sensor and throttle body but couldnt find any info on anyone having done it on the IS300H.

The maf sensor should be straight forward and i found videos for how to do it for the 2ar engine but for the Throttle body it seems like a bit more of an involved job and disconnecting the intake hose doesnt seem like a straightforward easy job. Any tips if anyone has done it would be appreciated.

Also when researching i found that this lean running when cold might actually be normal for hybrids as they do all sorts of weird stuff including running lean to heat up faster. But strangely I never noticed it before. Any thoughts?

wharfhouse · April 24

1 hour ago, Notamech said:

So yesterday I started my car drove on to the road and immediately got stuck in traffic. Given the engine was cold it was running as the car was trying to warm up. While sat in traffic I noticed something strange, at idle I could feel vibrations of the running engine in the cabin intermittently. The best way to describe it would be as if the car is running lean and was close to cutting out except it wouldn't cut out. when the car is moving its fine. Which got me thinking that given it has run 94k now perhaps as good practice it might be worth cleaning the MAF sensor and throttle body but couldnt find any info on anyone having done it on the IS300H.

The maf sensor should be straight forward and i found videos for how to do it for the 2ar engine but for the Throttle body it seems like a bit more of an involved job and disconnecting the intake hose doesnt seem like a straightforward easy job. Any tips if anyone has done it would be appreciated.

Also when researching i found that this lean running when cold might actually be normal for hybrids as they do all sorts of weird stuff including running lean to heat up faster. But strangely I never noticed it before. Any thoughts?

I sometimes get a bit of "hesitation" at idle as you have mentioned - it's as though the engine just needs a few more revs. Only seems to happen in certain use cases - usually when the engine is warming up and the EV mode is close to kicking in. It's done it occasionally since I have had the car (which was 2 years old with 40K miles on it when I purchased it - now it's over 9 years old with 146K miles) so I haven't worried about it.

IS300FSPORT · April 24

I wouldnt worry at all I have exactly the same experience.

More apparant when the Engine switches to EV mode.

Mines on approx 55k cleaned the MAF sensor, new air filter, spark plugs, throttle body cleaned.

Just to give you reassurance Iv seen a Camry Hybrid on 520,000 km in Dubai before now very reassuring. Lexus is more than capable of handling big miles if maintained that should put your mind at ease. The rust in the UK will likely rot it before the engine gives up.

Notamech · April 25

Yeah i did a lot of research on this and sounds like its normal. The ECU deliberately decides to run the engine lean to generate more heat faster. This made no sense to me as i always thought more fuel=more energy and hence more heat. But apparently that is not the case. A lean mixture generates more heat because there is a more complete burning of fuel taking place vs a rich mixture where relatively speaking more fuel is wasted also in a rich mixture the unburnt fuel conducts some of the heat away. So i guess it makes sense that under certain situations where power demand is low e.g in traffic and when the engine wants to warm up fast that the ecu decides to run it lean. Strangely i was in the same situation today but it didn't do it and everything was smooth as always.

Sometime in the next few weeks I'll still clean the throttle body, MAF sensor and replace the PCV valve just for good measure. Its also strange that cars these days dont come with replaceable fuel filters. Ive seen videos of people opening up the pump assembly to get at these "lifetime" filters and what comes out is nasty.

matt8 · April 26

On 4/25/2024 at 2:44 PM, Notamech said:

Sometime in the next few weeks I'll still clean the throttle body, MAF sensor and replace the PCV valve just for good measure.

Any chance of a small write up and some photos please, @Notamech? 😉

Notamech · April 26

54 minutes ago, matt8 said:

Any chance of a small write up and some photos please, @Notamech? 😉

Yes will definitely do a guide or a video. Just waiting for the weather to be more conducive. Its just been so cold lately. I seem to have figured out how to do it in theory at least. When i actually go to do it, as is often the case, new hurdles show up. This engine just seems so DIY friendly that im tempted to keep it forever.

Notamech · May 16

So i planned to do MAF + throttle body clean and replace the PCV valve. I ordered a new PCV valve on amayama and its finally here after 3 weeks or so. I am surprised at the price difference between lexus parts direct and amayama. The pcv valve costs £47 at lexus parts direct and it costs only 7usd and i paid 8 usd for shipping so less than £15 on amayama with shipping. Thats a massive difference.

https://lexuspartsdirect.co.uk/product/lexus-is-phase-3-pcv-valve/

https://www.amayama.com/en/part/toyota/1220436040

Anyway. Hopefully il find the time soon and make a DIY guide on it.

Notamech · May 19

So finally attempted this today. Got all 3 done in around an hour. Everything was super easy. Just for context mine is a 2014 executive with around 95k miles on the clock and I reckon this is the first time these tasks have been carried out on this car. Overall having now done it i can say while its fine to do as a DIY task it is by no means necessary especially if your car is around the same mileage as mine? as everything was quite clean anyway. I havent driven the car since carrying out the below tasks so cant say yet if it made any difference to how the car drives and feels but i suspect it will be the same. A more important DIY i feel would be cleaning the hybrid Battery fan and filter when i did that at 90k it came out really dirty and cleaning it felt worth it.

MAF sensor cleaning:

Tools Needed A phillips head screw driver. My screwdriver bit said P1 so i assume this is the size. You will also need some EGR / carb / MAF sensor cleaner ...basically something that wont leave a residue. Do not use brake cleaner or wd40.

Procedure

1. Unplug the maf sensor by pressing down and releasing the plastic locking tab and pulling the plug away.

2. Undo the 2 screws marked in blue and pull the sensor out. Be careful to not use the wrong size of screw driver and strip the screw heads as they seem quite delicate and if you damage them you will need new screws. Fortunately they were aluminium screws i think as they had white corrosion not rust.

3. Once removed make sure to clean the rubber seal/ o-ring with a clean towel. This o ring seals the sensor in the housing and keeps dust / dirt out but gets really dirty when removed. Also clean the outside of the sensor.

4. In an open well ventilated area spray some cleaner on the metal sensor wire. There are 2 of these metal bars with a resistor or something connecting them in between. Do not touch these bars with anything. Do not use a cotton swab / towel / brush or anything else to clean these bars. Only use the cleaning spray and let the cleaning spray and the pressure from the can do all the work. Use gloves and avoid the fumes from the cleaning spray.

5. There are 2 more sensor wires hidden inside spray these too. Once done let the sensor air dry in a clean ventilated area

Once the sensor has dried reinstall it. Do not overtighten the screws. Connect the plug back in

Notamech · May 19

Throttle body cleaning

Things you will need: A 10mm socket and a ratchet. Alternatively a phillips head screw driver might work. Needle nose pliars. The same cleaner you used for your MAF and a clean rag.

Before you begin I highly recommend watching the car care nuts video on throttle body cleaning a lot of it is relevant and will give you a very good overview into what you are doing and why and its implications.

Steps to get to throttle body

1) Pull up and remove engine cover.

2) Press the metal clip and pull back to release. The tension on these clips isnt too much. So you can just use your fingers to squeeze it. Squeeze it and pull it to the position you currently see in the picture

3) Now that the clip is off th spout. Wiggle the pipe while pulling it in order to disconnect it from the spout.

4) Unplug the MAF sensor as seen in my previous post. Once this is done you need to release the clip that holds the MAF wire loom on to the intake pipe. This can be done using needle nose pliars to squeeze the clip and push it out the hole. In my case the zip tie part of the clip came undone so the wiring loom was free.

5) Use the ratchet and 10mm socket to undo this bolt till you feel that the hose clamp is loose. As you can see this bolt also has a phillips head so you may be able to use a scredriver to undo this screw. When re-installing the torque specs for this bolt is 4nm but i didnt have a torque wrench that goes this low so i just tightened it what i thought was enough i.e not too tight.

6) Now undo the 5 clips on the air filter housing. Once you do this put your hand under the intake pipe assembly, just where it bends to go down to the throttle body and push forward. This should break the pipe free from the throttle body. Now just keep wiggling the pipe assembly forward and backwards while trying to pull it upwards and the entire assembly should lift off along with the top cover of the air filter box exposing the throttle body.

As you can see there was quite some carbon build up around and on the edges of the butterfly valve it wasnt excessive just a thin layer. For 94k i think this isn't bad at all.

Cleaning

Spray some cleaner on your rag and start wiping with your rag. Use your fifingers to push open the butterfly valve and clean thoroughly using different clean sides of your rag after soaking it in clener.

Do not spray cleaner directly into the throttle body you dont want that carbon going in you want it out.

Dont use metal screwdrivers etc to keep the butterfly valve open you could cause damage.

When pushing open or closing the butterfly valve make sure to be gentle. The spring action on the valve is quite strong so dont just let it go. Slowly release it to close when cleaning on the under side of the valve or around the throttle body walls on either side of the valve.

Once done re assembly is just the reverse. Remember to connect back the hose you disconnected and plug in the MAF sensor.

Overall i guess it is good to do this once in a while.

Notamech · May 19

PCV Valve replacement.

Things you will need: A medium sized torque wrench or ratchet. I used a small ratchet initially but it didn't provide enough leverage to break the pcv valve free so recommend a medium sized one. A 19mm deep socket. A new PCV valve. Loctite red 271 threadlocker this is equivalent to threebond 1324 or toyota 1324 that toyota recommends for this job. A rag.

Note: I bought bought my pcv valve for ~£15 on Amayama shipped. Given how non urgent this job is i believe this is the way to go if youre doing this job. Dont go spending £50 on Lexus parts direct. When i uninstalled my old pcv valve it was still in good order and changing it was completely unnecessary. Online the recommendation seems to be to change this every 30-40k maybe thats true for non toyota vehicles. The valve mechanism on mine seemed as free as the new one, if i shook it, even after ~95k miles. I did not notice any signs of clogging or gummy residue that could clog it anytime soon.

How to:

1) Remove engine cover by lifting up as explained in previous post.

2)Press the clip to loosen and move it further down the pipe so that it is no longer clamping on the PCV valve spout.

3) Wiggle the hose while pulling it away to remove it from the PCV valve.

4) Using your ratchet / torque wrench and your 19mm deep socket undo the old PCV valve by turning anti clock wise.

5) Once the old one is removed you will see a bit of dark oil deposits on the old valve and the hole from which you removed the valve. Use some egr / carb cleaner and a rag to clean the threads in the hole. Again do not spray directly into the hole. Wet a rag with the cleaner and push that into the hole to clean the threads.

5) Get your new PCV valve and dab some threadlocker only on the bottom few threads this is because some of the top threads stick out of the hole by design. I looked up the equivalent for the recommended threadlocker and the loctite red 271 seems to be one thats equivalent and is also easily available (on amazon for £11) vs the threebond 1324 or toyota 1324 which is the same thing rebranded and not easily available.

6) Start installing by hand in order to avoid cross threading. Turn clock wise to screw in the new pcv valve. Once you cant turn it by hand anymore use your torque wrench. Set it to 27nm and start tightening the pcv valve. Stop when the torque wrench clicks.

7) Wipe off any excess threadlocker / spills with a rag.

8 Reconnect hose and slide the clip back into position.

9) Reinstall engine cover. You can spray some silicone spray into the rubber boots of the engine cover to keep that rubber supple.

It is recommended that you do not start the car for at least an hour after installing in order to allow the threadlocker to set.

I started the car after an hour and no check engine lights or anything. Everything functioning as intended. I didn't drive though. Will see if this has made any difference to the overall feel / smoothness etc. tomorrow. Will report back if there is a difference. The idle rpm was between 1000 and 1100 but i only ran the engine briefly and perhaps thats normal for a cold engine or it could be due to the computer having to re-learn the ideal throttle position for idle after the clean.

dazzlar · August 2

@Notamech fantastic write up, thank you very much for taking the time to do this. I've just given my car a service now at just under 105,000 miles and thought it's probably about time I gave the throttle body a clean. I'll be doing this, and the MAF clean, so glad to find a guide (not that I expected it to be difficult). How did your PCV valve seem when you removed it. I'm not getting any issues so thinking I leave that, I hardly do any miles since covid and WFH, but maybe if yours looked like it needed it I might just do it for the sake of a few quid.

Notamech · August 2

5 minutes ago, dazzlar said:

@Notamech fantastic write up, thank you very much for taking the time to do this. I've just given my car a service now at just under 105,000 miles and thought it's probably about time I gave the throttle body a clean. I'll be doing this, and the MAF clean, so glad to find a guide (not that I expected it to be difficult). How did your PCV valve seem when you removed it. I'm not getting any issues so thinking I leave that, I hardly do any miles since covid and WFH, but maybe if yours looked like it needed it I might just do it for the sake of a few quid.

Yeah you can leave the pcv valve. I did it for good measure as advice on the internet seems to suggest that its good to change it at 30k i guess thats probably true in the us or other places for other brands. The old pcv valve that came out was still good and rattled like it should. A more important DIY is to clean your hybrid fan and filter its important for your Battery health and when i did mine at around 93k or something it was super dirty and cleaning it felt worth it.

dazzlar · August 2

3 minutes ago, Notamech said:

Yeah you can leave the pcv valve. I did it for good measure as advice on the internet seems to suggest that its good to change it at 30k i guess thats probably true in the us or other places for other brands. The old pcv valve that came out was still good and rattled like it should. A more important DIY is to clean your hybrid fan and filter its important for your battery health and when i did mine at around 93k or something it was super dirty and cleaning it felt worth it.

Thank you for replying, that's good to know, yeah, I've done the hybrid filter at 50 and 100K, both times mine was really clean, which I'm surprised at as I'm not particularly car proud, and often fill the car with DIY stuff and rubbish etc. The other thing I've found on mine (sure it's probably mentioned on this forum), is the air filter drain is on top of the body so worth removing the air box and checked for corrosion underneath (salt spay water drains here in winter). I'm thinking about 3d printing a diversion hose so it drains to a more appropriate location if I can be bothered! I've had the car since new, and not sure if I want to replace it, but it's been so good, I don't normally keep them this long, just which it was a bit more practical and exciting.

Notamech · August 2

12 minutes ago, dazzlar said:

Thank you for replying, that's good to know, yeah, I've done the hybrid filter at 50 and 100K, both times mine was really clean, which I'm surprised at as I'm not particularly car proud, and often fill the car with DIY stuff and rubbish etc. The other thing I've found on mine (sure it's probably mentioned on this forum), is the air filter drain is on top of the body so worth removing the air box and checked for corrosion underneath (salt spay water drains here in winter). I'm thinking about 3d printing a diversion hose so it drains to a more appropriate location if I can be bothered! I've had the car since new, and not sure if I want to replace it, but it's been so good, I don't normally keep them this long, just which it was a bit more practical and exciting.

Totally understand. Even i struggle to think of what to buy next. My usage is also very low <5k a year so might just drive this till the wheels fall off but on the other hand i do feel the need to experience something new..so might move to an NX 300 or GS450 in a couple of years depending on my needs at the time.

dazzlar · August 2

I thought the bonnet latch needed attention when I serviced it, but was in a rush so ignored it...

wharfhouse · August 2

2 minutes ago, dazzlar said:

I thought the bonnet latch needed attention when I serviced it, but was in a rush so ignored it...

I had to have mine seen to on my 2014 IS 300h. It started by not latching intermittently and over about a year finally gave up completely. Happened to be in for a service with Lexus when it failed so they cleaned it up and replaced one of the springs. It's been working fine since. Others have mentioned problems with this latch too around a similar age so obviously something that needs a bit of attention when approaching 10 years old.