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.