Rx300 Throttle/gearbox Response

abecketts · December 27, 2015

Hello,

We've had our RX300 for a couple of weeks now and whilst enjoying it i'm wondering is it normal to feel as is the throttle response is at times weak/vague or then more full on when doing normal driving. Add to that sometimes the gearbox seems to be hunting for the right gear when you move away or accelerate. I maybe overplaying things but are RX's prone to throttle or gearbox issues? Apologies if my powers of description are a little below par.

Thanks

rayaans · December 28, 2015

The 2nd gen RX300 does have a somewhat hesitant gearbox at times and will lurch forward sometimes. I had one before my RX450H and I can remember this very well but it never had too much impact on me. I think it is having more of an impact on you down to the coupling with the sluggish response you describe

The RX300 had great throttle response. Could be anything e.g. clogged fuel filter, fuel pump, fuel lines or faulty oxygen sensor

I'd be inclined to think the oxygen sensor is playing up as its a common thing but then I'd also expect the check engine light to be on. I'd get the car checked by a mechanic first buddy

PCM · December 28, 2015

Maybe the time to locate a good, recommended, local Lexus type specialist, independent garage.

Someone that will get to know your car, and look after it as you do...

PCM · December 28, 2015

PS. Mine can be a tiny bit hesitant at times...

I think I just changed my driving style and expectations slightly...

( I did get the trans fluid changed also, by my ... "local Lexus type specialist, independent garage"

What's the milage?

abecketts · December 28, 2015

PS. Mine can be a tiny bit hesitant at times...

I think I just changed my driving style and expectations slightly...

( I did get the trans fluid changed also, by my ... "local Lexus type specialist, independent garage"

What's the milage?

Hi, appreciate the feedback, car has 79k on the clock, I will get the car checked over by our garage as they have the diagnostic kit and whist the gearbox oil is nice and red it probably could do with a change. It is a very comfy car that accommodates the 5 of us and has space enough in the back for 2 6'4" teenagers to sit comfortably.

ChrisKaye · December 28, 2015

Sounds like your MAF sensor and air filter could do with checking and a clean (I'll be doing mine soon and will try and get some pictures) - start with the simple things.

As for the gearshifts, I have noticed that it can be confused (hardshift) when slowing down to about 10-15mph (approaching a mini-roundabout, for example) and then accelerating to get back to 30mph if there is no traffic and you don't have to stop. This doesn't happen if you put it into sports mode and manually control the gears but is cumbersome and not practical it must be something to do with the shift program in the ECU and is probably more noticeable in the UK/Europe than the US (due to road layouts & lack of roundabouts!)

PCM · December 28, 2015

Sounds like your MAF sensor and air filter could do with checking and a clean (I'll be doing mine soon and will try and get some pictures) - start with the simple things.

As for the gearshifts, I have noticed that it can be confused (hardshift) when slowing down to about 10-15mph (approaching a mini-roundabout, for example) and then accelerating to get back to 30mph if there is no traffic and you don't have to stop. This doesn't happen if you put it into sports mode and manually control the gears but is cumbersome and not practical it must be something to do with the shift program in the ECU and is probably more noticeable in the UK/Europe than the US (due to road layouts & lack of roundabouts!)

This??? http://www.mafcleaning.co.uk/

ChrisKaye · December 28, 2015

Yep, I have some good electrical contact cleaner spray already that I've used before to clean a MAF on our Celica, so saves having to buy anything! It's important to use one that leaves no residue once dried.

ChrisKaye · December 28, 2015

I'll see if I can dig up a post from elsewhere on checking air filter and cleaning the MAF on an RX...

ChrisKaye · December 28, 2015

So oddly can't find any posts with pictures for the Mark II RX 300 for cleaning the MAF sensor!

I did see on another post that a dirty MAF can interfere with shift points on automatic boxes:

"In many cars the air flow sensor signal is used to determine automatic transmission shifting points. A problem with the airflow sensor could alter the shifting pattern of the automatic transmission."

So will be interested to see what (if anything) it does to mine!

ChrisKaye · December 28, 2015

Right, just cleaned my MAF and IAT (Mass Airflow and Intake Air Temp sensors).

See pics below.

Pop off the connector to the MAF, by depressing the little tab above the wires and gently wiggling it as you pull the connector towards the windscreen.

Carefully unscrew the MAF from between the air filter box and throttle body. It has 2 Phillips head screws - find the best fitting screwdriver you can for this job, these screws are notoriously soft metal! Once undone, pop into your pocket to keep them safe.

Pull up on the MAF and the little unit will pop out so you can take it over to your work area to clean it with contact cleaner or MAF cleaner spray.

The MAF "wires" are inside the tube so just liberally soak a few times.

Using a cotton bud and cleaner, clean the IAT so it is browny/red and shiny. Do not use force on the cotton bud, just gentle wipes.

Using a rag or kitchen towel, clean the plastics to remove grime, dust and debris from the body of the sensor.

Clean the screw heads to make the screwdriver fit better when re-installing.

Leave the unit somewhere warm for 10-15 minutes (or blast with a hairdryer on low heat) to ensure all cleaner has evaporated before re-installing.

Clean the hole where the MAF fits into to ensure the MAF seals back into the top of the assembly. Gently put the screws back in and tighten down, hardly any torque is required so don't over tighten them, you'll strip the heads!

If you have dielectric grease, pop some on the connector and reattach it.

I've not reset my ECU and this maybe necessary, I'm going on a quick test drive and will report back!

ChrisKaye · December 28, 2015

Just back from a 5 mile test drive and full refuel from virtually empty. Engine slightly smoother, too early to tell regarding shifting.

I was gating around 25mpg from a tank and have a 30+ mile journey later today so will see if mpg improves any.

My MAF didn't look too bad and the ECU didn't seem to care.

Other posts I have read have stated that if you're MAF is totally replaced or very clogged & cleaned, when you start the car after it may run rough as it is still compensating for the original problem which should now be fixed - if this happens to you, the ECU should be reset by taking the Ground wire off the Battery for 20+ minutes which will make the ECU erase it's memory and re-learn the individual car and driver's characteristics.

Resetting the windows and moonroof and radio is a bit of a pain so I am happy to not have to do that!

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ChrisKaye · December 28, 2015

I'm back from a 34m round trip of urban and rural roads and I think the shifting has improved - there were a few occasions where I was sure I'd get a hard shift but smooth as silk, mpg was 28.6mpg and I wasn't driving miss Daisy all the time!

I think I'll check tyre pressures tomorrow as it's been a couple of months to see if they are all still at 33psi (which for me is the best trade off between economy and comfort!)

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