Throttle/fuel feed issue

[Neilado]

Hi all,

I'm lucky enough to have inherited my Dads SC430 after he recently passed away. It’s always had an issue with the revs and accelerator pedal. Initial pulling away is lovely but as yr driving at a constant speed as little as 40mph, the revs will suddenly drop away and you’ll have to make up the shortfall by pushing down again. I don’t know whether it’s a fuel feed issue or a mechanical pedal thing. Local garages and a dealer have checked it and found nothing ... Any ideas ? Otherwise the car is fantastic ! 
thank you

 

[royoftherovers]

Welcome Neil.Enjoy Membership and the SC.

Our resident SC experts will pick up your arrival soon and suggest remedies I am sure.

[steve2006]

Hello Neil, welcome to the LOC, and please accept my condolences on the loss of your Dad.

It seems a little strange that a garage with the correct diagnostic equipment didn’t find any fault codes which would help pinpoint the problem.

The electronic throttle body is termed “Drive by wire” so there is no physical throttle cable between the pedal and the throttle body. Instead there is a pedal position sensor which detects the position of the pedal, a throttle position sensor on the throttle body which senses the position of the throttle butterfly, a motor to operate the butterfly and a computer between the 2 which performs communication and controls operation.

Without any diagnostic codes finding the cause of your problem is not as easy but I would start at the accelerator pedal sensor which is fairly easy to access and check. Look to make sure it is firmly attached to the support bracket, it is plugged in firmly to the loom and the loom is undamaged.

The picture below should help you find it, N3 is the sensor in question.

[m4rkw]

2 hours ago, Neilado said:

Hi all,

I'm lucky enough to have inherited my Dads SC430 after he recently passed away. It’s always had an issue with the revs and accelerator pedal. Initial pulling away is lovely but as yr driving at a constant speed as little as 40mph, the revs will suddenly drop away and you’ll have to make up the shortfall by pushing down again. I don’t know whether it’s a fuel feed issue or a mechanical pedal thing. Local garages and a dealer have checked it and found nothing ... Any ideas ? Otherwise the car is fantastic ! 
thank you

Does making up the shortfall always work consistently or do you find you sometimes have to push it significantly more to keep the revs up? If the former I'd suspect an electronic issue with the throttle pedal, wiring or signal. If the latter I'd suspect a fuelling issue.

[Neil E]

A Lexus dealer or someone with access to Toyota Techstream should be able to identify any existing fault codes. Presumably it isn't showing a check engine light.

Do the revs actually drop on the tachometer or does it just feel like the car is being starved of fuel?

If local garages and a dealer has found nothing then I would assume they have looked at all of the usual and obvious issues with fuel and air, MAF sensor, loose fittings and cleaning etc. It seems a rare complaint but there is one similar instance noted in the US that I found and that turned out (in the end) to be the throttle position sensor as suggested above by Steve. 

I know from the experience of adding a Sprint Booster it's a very good secure plug system so unlikely to come loose. It's not too difficult to access if you're supple (which I'm not) viewing it and the wiring might be easiest with a mirror in the foot-well. 

 

 

[ColinBarber]

Ideally you need some diagnostic equipment with data logging capabilities so you can take real-time readings of the engine parameters and sensors whilst driving and then go back and look at the data so see what the issue is. It is very obvious for example if the throttle position sensor reading suddenly changes, or a temperature sensor etc.

[Neilado]

Thank you all for yr replies - love the tech detail. Exactly why I joined.

regards

Neil

[Bugsbunny]

Just clean the throttle body sensor... Open hood, slide airbox off, remove sensor and spray with cleaner. 

Then reset ecu procedure or remove Battery for a while. 

They all do this if not driven often, use it for a week or 2.

[JeffbC]

Neil, my 2002 Does the exact same thing as your Dads car. We’re you ever able to find a solution? Would love to know! Thanks