Rx400h Cruise Control - Sudden Unexplained Acceleration

rishishah · February 25, 2010

I have an 07 RX400h SE-L. When i drive it in cruise control at 70MPH on the motor ways no problems and it behaves. Last weekend i got a chance to drive it at 50MPH in cruise control on some A roads and this was probably the first time i did this at this speed. However every now and than the car would suddely accelerate for no apparent reason although it was set to 50 and i will touch the cruise control leavers.

Now if there was a hill, i would appreciate the car would need some more power to keep the 50MPH speed constant, but this was on a flat road. There is a US Lexus Official Service Bulletin for this (EG013-07), but my dealer has confirmed that this does not apply in the UK.

As this is first time it has happened i will try and replicate it again this weekend on some empty roads before taking it to the dealer so that i can be sure i can replicate the issue with him in the car.

Has anybody seen this on a 07 RX 400h?

Many thanks,

Rishi

lfoggy · February 25, 2010

Are you sure its actually accelerating and its not just the engine revs rising due to the gear ratios changing in the gearbox? If its accelerating, by how much does the speed actually change ?

ihpj · February 25, 2010

Are you sure its actually accelerating and its not just the engine revs rising due to the gear ratios changing in the gearbox? If its accelerating, by how much does the speed actually change?

It could be charging the hybrid Battery so it seems like a surge but its only revs increasing?

Without more, hard to comment!

rishishah · March 15, 2010

Are you sure its actually accelerating and its not just the engine revs rising due to the gear ratios changing in the gearbox? If its accelerating, by how much does the speed actually change ?

No it is actually accelerating...so if i am on 50MPH it will go upto about 57MPH before i physically brake (too afraid to let it go futher). Another thing i can also replicate is on cruise control if i turn the car by more than a 30Deg bend or so the car will again start to accelerate.

Can anybody try these tests and confirm if they see it on their RX400h while in cruise.

lfoggy · March 16, 2010

I've never had that problem on mine and I use cruise regularly. Sounds bizarre and potentially dangerous. I would definitely take it to the dealers as soon as possible.

Parthiban · March 16, 2010

I heard this was one of the problems on the prius and an apple guy was having this exact problem with his car. Can you replicate it or does it happen intermittently? If you can I'd get a dealer to experience it to show him what a moron he's being as that sounds like something that needs attention.

rishishah · March 20, 2010

I heard this was one of the problems on the prius and an apple guy was having this exact problem with his car. Can you replicate it or does it happen intermittently? If you can I'd get a dealer to experience it to show him what a moron he's being as that sounds like something that needs attention.

I can replicate this between 40MPH and 50MPH on A/B roads especially where there is a turn in the road. It will accelerate by itsself. I was hoping others could try too.

rishishah · March 25, 2010

I heard this was one of the problems on the prius and an apple guy was having this exact problem with his car. Can you replicate it or does it happen intermittently? If you can I'd get a dealer to experience it to show him what a moron he's being as that sounds like something that needs attention.

I can replicate this between 40MPH and 50MPH on A/B roads especially where there is a turn in the road. It will accelerate by itsself. I was hoping others could try too.

Well the car has gone in for the check up today. Lets see what they say after they replicate the issue.

However if anybody else out there could try it (if its safe to do so) just to make sure that we dont have a big problem on our hands as RX400h owners. For me it happens between 40 and 50MPH in cruise and especially when the car turns more than 30Deg while still in cruise and damn the sudden acceleration starts.

Update: Dealer's Service Manager cannot see any issues. I am frankly very surprised as i know the issue is there.

Will keep on monitoring and logging it. Anybody else who uses Cruise in A/B roads see anything i have described. Seems that other CVT Toyota engines in the US do this a lot too during Cruise, however for now Toyota in the US is describing this as within tolerances.

lfoggy · March 26, 2010

I did a long drive on B roads today and used the control set at around 50mph. The indicated speed was rock steady an didn't vary apart from speeding up on the occasional steep down hill. Cruise is not really designed for this type of driving though. On the straight bits 50mph was too slow and on some of the bends it was too fast with a peculiar sensation of accelerating into the corners. Personally I would only use cruise on motorways etc....