RX300 Air intake problems

[sorcerer]

Just happened to notice this earlier on this afternoon. I'm assuming that that rod should be inserted in that green bush and that it somehow controls some sort of flap mechanism or something but without a service manual it's just guesswork. Can anyone shed any light on it and let me know (a) what it should do and (b) what the car is probably failing to do at the moment, that it should and would be doing, if that push rod was properly located?

[ChrisKaye]

Hi, please see attached photo of my RX.

The tube should just push fit into the green retainer on the brown part on the throttle body.

I'll see what I can find out...

First guess would be it is a vacuum operated lever that may open the Throttle plate wider when VVTI kicks in at higher RPMs, failing that, idle speed or emissions control.

Any symptoms of funny behaviour?

C.

[ChrisKaye]

Right, that's in a funny part of the EPC, under Manifold!

The part is 17300-20020 and is a "VALVE ASSY, INTAKE AIR CONTROL" - it does look to be operated by vacuum from the manifold. The guide/breakdown of the part is here:

http://www.japan-parts.eu/lexus/eu/2003/rx300-330-350/mcu35r-awagkw/3_521220_002_235W/tool-engine-fuel/1701_manifold

It's in the centre at the top of the diagram.

Whilst no doubt important, I don't think it is a critical component as would most likely lead to rough idle/running but if the computer senses this part is not working, it will be compensating via the software so you may not notice this issue at all if the car has always been this way since you had it.

Patch it back together and see what happens!!

C.

[sorcerer]

Hiya Chris and sorry for the late reply, been away for a few days but thank you for your very informative input.

The car is running perfectly alright with no roughness at all, either at speed or when just idling, but to my non-mechanical mind it's all a bit of a mystery what's going on. The push-rod is now back in its little green retainer and is free to move but I'm not sure when it should move. I've had the car stationary on the driveway and revved the engine up to over 4,000rpm but no movement occurs. I've also moved the assembly by hand whilst the engine is running but it has no effect - engine still runs smoothly with no lumpiness, stutters or roughness.

One of the problems I've got is that I've never had, or driven, a Lexus RX300 until getting this one so I have nothing to compare it to. One area I'm not too sure about and it may or may not have anything to do with this 'Valve Assembly, Intake Air Control', is fuel consumption. Before the LPG conversion the best we had on petrol on a run was 28mpg (according to the onboard computer) and the best around town was 17-18mpg, which would seem a bit low maybe? I'm comparing it to my old Nissan Maxima QX which was a 3.0 V6 auto, the same as the RX300, and gave about 32-33 on a run and about 23 around town. Now, I do realise that the RX300 is a much bigger and heavier car, but I'm wondering if size and weight alone can account for the difference or if this Intake Air Control has comething to do with it too?

Another area I'm not sure of is the 'drive by wire' system. The Nissan was SO responsive - on the German autobahns with a fully-loaded car, already doing 80mph, I could put my foot down and we would be thrust back in our seats, and just mere seconds later we'd be doing over 110mph. Ok, that's an extreme example and not something you do in every-day driving but you get my point. Putting my foot down in the RX300 seems to elicit a 'thinking time' of a second or two before there's any response sometimes. Again, I don't know if that could be anything to do with this part or if that's just how drive-by-wire systems work?

Cheers,
John

[ChrisKaye]

Hi john, I mainly do 20m of b-roads (no traffic lights) to work and average 28 at the mo, I try to avoid traffic & city driving so can't comment on that mpg figure.

I don't think the RX drive by wire is the problem but the gearbox (or programming) is slow to shift and frequently gets confused when driving in a spirited fashion and slowing for roundabouts then planting it again cos the coast is clear. I've gotten used to the quirks and tend to take control using the S mode on the gear box, once you know how that works (it's not tiptronic but limits the highest gear the car will use) you can force the right gear for the occasion.

When driving sedately, the gearbox comes into it's own with smooth, gentle relaxing shifts.

As for the valve assembly, no idea! If I ever take mine apart and figure out what it does, I'll be sure to post it.