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Hi all, first post here.

I bought an '04 RX300 a couple of months ago and have recently changed the A/F sensor on bank 2 to cure a P0430 code and an insatiable thirst (12 mpg average!). It seems to have been successful but the car is now kangarooing on moderate acceleration between 2000 and 3000 rpm. Bank 1 A/F sensor has been changed this week which has improved things slightly.

I've tried to locate the IACV to clean it but my car's throttle body looks nothing like the pics I've found which seem to be US RX300s and have dual throttle bodies. My car has a single throttle valve. Idle speed is fairly steady and the car doesn't stall.

Carb cleaner hasn't made much of a difference, neither has an Italian service.

Any ideas welcomed!

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The US RX series II was different to the UK in that the RX300 wasn't sold, the RX330 used a different engine.

If you were running that rich to only get 12 mpg then I would have a look at one of the plugs to make sure it isn't fouled up. Cleaning the MAF sensor, throttle body and checking the throttle position sensor is adjusted correctly would be my next steps. The IACV wouldn't normally cause the problems you are experiencing.

Are you using genuine Denso A/F sensors?

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I probably should've mentioned that it's running on LPG! So around 14-15mpg equivalent, which still seems thirsty. (It has the same issues on petrol so it's not the LPG system at fault).

I've replaced the MAF sensor with a second hand part today and that's helped quite a bit. The A/F sensors are Denso DOX-0243 from sparkplugs.co.uk. The plugs in bank 2 were changed 30,000 miles ago and look slightly sooty but otherwise OK (haven't even attempted bank 1!).

Is there a guide anywhere for checking and adjusting the TPS?

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Bumping with a supplementary question!

Is there any information online about the differences (if any) between 99-03 and 04-07 UK spec RX300s? I've found some info about US models but hardly any for UK ones so far. Looking at what few part references I can find it looks like I might have fitted A/F sensors for a 2003 model.

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Update - a helpful chap at Denso UK has confirmed that DOX-0243 isn't compatible with 2004MY. The correct part, Toyota 89467-48050, is only available in the UK at the moment as a grey import (or cheap copy!).

Sensible offers accepted for 2 x nearly new DOX-0243 with a couple of hundred miles on...

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Hi Carl

mine is a 2001 model year, Denso also say dox 0243 is not suitable for RX300 Mark 1, it is!

Now Im not saying that it is compatible with your car, but if I was you Id call your local Lexus Dealer, and ask for the part number for a Mk1 and a mk 2 oxygen sensor, if its different flog em, if its the same put em back in!

Just my 2 penneth!

Cheers Jason

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Toyoparts lists the A/F sensor for Mk1s as 89467-48011 (which seems to cross reference to Denso 234-9009 and DOX-0243) and for Mk2s as 89467-48050. I've also been advised by Denso that the core of the sensor and the calibration of the signal differs between these parts.

Although the sensors fitted to the car at the moment are apparently the wrong ones they haven't thrown a CEL, surprisingly.

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Hi

Normally if the sensors are not creating a CEL, they are transmitting the correct parameters to the ECU, I appreciate they are different part numbers, but different part numbers for same part between models not unheard of, my father in laws 200tdi Disco needed a new headlight, £240 from Land rover, £47 from Rover, shared part with Maestro!

I MUST REPEAT, I am not saying Denso man is wrong, but at same time would nt be super surprised,

let us know how you get on, so other people can benefit from your experience.

Cheers Jason

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Yeah, to say there are quite a few RXs knocking around there doesn't seem to be much definite info out there. My old Volvo V70 was never this difficult to source spares for...

The best way I can describe driving the car is it's 'not quite right' - when cruising or flooring it the car is fine but under moderate acceleration it feels like the throttle is being applied then released roughly twice a second. The parts are due Saturday so by Sunday or Monday I should know one way or the other!

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Hi Carl
Does the problem happen when running on petrol also?

Have you checked your coils?

Have you tried an ecu reset?

My RX300 did over a year with bank 1 and 2 sensor fail, I lost 2 mpg and had a CEL, if it wasnt an MOT fail I would have left it longer ( was looking at over £600 at Lexus main stealer) but it drove perfectly, I just cant see the sensors causing your symptoms, it would be under all driving conditions!

Cheers Jason

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Hi Jason, my answers in blue...

- Does the problem happen when running on petrol also?

Yes.

- Have you checked your coils?
No - is there an easy way of checking them? (Especially bank 1...)
- Have you tried an ecu reset?

Yes (only very slight improvement.)

I suspect it's related to the A/F sensors as the problem only started when I changed them - the throttle response is much better but the kangarooing on acceleration can't be good for the engine and transmission, and spoils what's otherwise a very nice car to drive.

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Hi

researching further coils seems unlikely, would cause a uneven idle too, Ive looked all over the net, cant find ANYTHING on any car that exactly matches your symptoms, some throttle position sensor faults cause similar problems but not the same, also found a couple of reports of faulty alternators causing pulsing on engines when driving along!

I hope changing the sensors fixes your problem, cos if its not I wouldnt be sure where to go next!

Cheers/ Good luck

Jason

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Slight misfiring on acceleration is a very common condition for a misbehaving coil pack and it would idle fine. However it is unlikely to be this given that the issue only started when the air/fuel ratio sensors were replaced.

I'm not surprised you haven't found these symptoms listed - installed sensors for another engine wouldn't really be seen as a likely scenario ;)

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Hi

researching further coils seems unlikely, would cause a uneven idle too, Ive looked all over the net, cant find ANYTHING on any car that exactly matches your symptoms, some throttle position sensor faults cause similar problems but not the same, also found a couple of reports of faulty alternators causing pulsing on engines when driving along!

I hope changing the sensors fixes your problem, cos if its not I wouldnt be sure where to go next!

Cheers/ Good luck

Jason

Cheers, I'm a bit stuck too as I've also done a bit of searching and got similar results! Will update when the new sensors are in, hopefully early next week.

Slight misfiring on acceleration is a very common condition for a misbehaving coil pack and it would idle fine. However it is unlikely to be this given that the issue only started when the air/fuel ratio sensors were replaced.

I'm not surprised you haven't found these symptoms listed - installed sensors for another engine wouldn't really be seen as a likely scenario ;)

Heh, fair point :-)

The bizarre thing is that it's the same engine (Toyota 1MZFE) but it seems like the ECUs in pre and post 03 models are configured slightly differently. Toyota didn't think to change the physical fit of the sensor nor its electrical connector so it's as easy to fit the wrong part as the right one (I dare say plenty of other manufacturers do this too...).

I've driven misfiring cars in the past and it doesn't feel like that, more like it's in a cycle of over and under fuelling but only in particular states of acceleration, which from a layman's perspective would tie in with problems in the fuel map.

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There must be some difference for Denso to bother selling different aftermarket parts. That difference could be something as small as a difference in lead length to take into account different wiring loom positions but your contact at Denso seems in indicate something different. The series I RX was one of the earlier Toyota/Lexus vehicles to use air/fuel ratio sensors rather than standard O2 sensors and there haven't been overly reliable so I'm not too surprised if they were reworked by Denso.

The 1MZ-FE has had two or three major reworks in its 12+ year life, you shouldn't just assume parts to directly fit between revisions, or even year to year although the majority of parts remain unaltered. One of those major revisions was between the series I and series II RX300 in 2003 - intake and exhaust systems were altered to improve emissions, and along with a different gearbox means heavily remapped ECU.

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Interesting stuff - thanks Colin. Are there any online resources with this sort of information for UK RX300s? Most of what I've found has been for pre-03 models and mainly US ones, which have some pretty major differences.

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There aren't many differences between the US and UK series I RX300s. The differences you are seeing are mainly the differences between the series I and II.

There isn't too much info about. The best source is the official repair and technical manuals from Lexus. Spend a couple of £ and subscribe for an hour or two:

http://www.lexus-tech.eu/default.aspx

the new car features docs may provide info on some of the engine changes but it's unlikely to go into the detail about differences in lambda sensors.

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Hi

cant believe that Carl, but back to my Toyota part number point, the Dox 0261 has 4 seperate toyota part numbers for exactly the same part!

Seems to be an Avensis, Camry part, hope they refund your postage too!

cheers Jason

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Toyodiy.com list the correct sensors as:

9467B SENSOR, AIR FUEL RATIO

89467-48050 NO.1 1 € 271.54

89467-48060 NO.2 1 € 271.54

As the RX300 series II doesn't exist in the US you won't find the vehicle listed. However the Toyota part code 89467-48050 show as being used on the RX330 and the ES330 and others too (including the 400h). I'm guessing that 48060 probably just has a slightly shorter or longer lead.

234-9042 seems to be the correct replacement for 48050. You certainly don't want anything DOX.... as that is a European part code.

RockAuto.co.uk / Rockauto.com would be my preferred supplier.

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Spoke to a chap from World Car Parts who said it was the correct part but was happy to accept a return for refund after I explained the problems I'd had and Denso's response.

The parts are now on order from Rock Auto so third time lucky maybe...

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  • 2 weeks later...

The problems were definitely down to the wrong sensors. Fitted the correct ones yesterday and it's running like a dream now, silky smooth. Thanks for all your help chaps! :phone:

The previous (new but wrong) sensors seem to be OK so they're going on eBay next week - sparkplugs.co.uk basically said 'sorry but tough' so caveat emptor.

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