Technical Car feels like it's accelerating and decelerating on its own

[deano87]

When sitting at a constant speed, say 70mpgh in 6th, the car feels like it's accelerating and decelerating on its own. It's ever so slightly though. Initially I thought it was because it's fly-by-wire and therefore more sensitive than my previous Corsa B 12v throttle, but I'm certain this is not the case now and something is wrong.

Also, it seems to use more fuel than I thought it would and I'm not driving that hard - someone mentioned lambda sensor - would this cause an increase in fuel and the accelerating/decelerating issue?

Main problem is the accelerating and decelerating though. Any help, advice etc would be great.

(I have searched for lambda sensor and accelerating/decelerating but didn't turn up much relating to my problem).

 

[adamcot]

If there was a problem with the lambda, you would have the "Check Engine" warning on the dash board. Im not sure what could cause the deceleration problem, possibly a faulty brake switch? Has someone followed you recently who would have noticed wierd brake light problems?

 

[Ffoxy]

Probably worth checking the induction side of things is as should be in terms of pipework security & tightness, a leak on induction could cause surging as described.

 

[deano87]

If there was a problem with the lambda, you would have the "Check Engine" warning on the dash board. Im not sure what could cause the deceleration problem, possibly a faulty brake switch? Has someone followed you recently who would have noticed wierd brake light problems?

Could it not be the lambda wearing out before it actually fails? And it's more a surge of power and the decelerating is 'natural', can just tell the brakes aren't being applied.

Probably worth checking the induction side of things is as should be in terms of pipework security & tightness, a leak on induction could cause surging as described.

Probably a good shout - I'm no mechanic though still got 3 months warranty remaining on the generic one I got with the car, plus it isn't 3 years old yet. Might book it in but not sure if I can be arsed with the hassle.


Anyone else any ideas? Car feels like it's surging and decelerating of its own accord, rather than braking.

 

[NachtDerUntoten]

Might book it in but not sure if I can be arsed with the hassle.

But still, better to get it checked over while in warranty than have something fail outside of warranty period - landing you with a bill.

 

[adamcot]

Could it not be the lambda wearing out before it actually fails? And it's more a surge of power and the decelerating is 'natural', can just tell the brakes aren't being applied.

If the switch is faulty, the brakes won't be applied. It will however cut the throttle back, as the ECU doesn't let you brake and accelerate at the same time. This could be the deceleration.

 

[Tym]

Just get warrantydirect policy to cover you after your 3rd year has finished!

 

[deano87]

Just get warrantydirect policy to cover you after your 3rd year has finished!

My girlfriend had one of those for a short period, it was rubbish. They blame everything to wear and tear therefore do not cover it.

If the switch is faulty, the brakes won't be applied. It will however cut the throttle back, as the ECU doesn't let you brake and accelerate at the same time. This could be the deceleration.

Well, when I say decelerate, it does that gradually. So your point is valid, but the 'braking' isn't much, it's more the surge of power.


I wonder if it's may be a blocked fuel filter because when I picked the car up, it had zero fuel in it, the range was ---- and I had to drive it a few miles to get some fuel.

 

[DilipVasan]

Hey
I'm facing the exact same issue on my brand new Punto btw is the fuel filter culprit in your case as even my car was almost empty when i took delivery