Jerky acceleration whilst in motion

[bobtail264]

I have had a Y reg Sovereign 4.00 for 17 months and find that depressing the accelerator (example - slowing at roundabout and accelerating to enter) the result is less than smooth. It is not wildly serious but I also have a Volvo V70 which is much smoother - I don't think this should be! Mentioned this to an independent local Jaguar facility and they cleaned a cable (?) entering the gearbox and it red]seemed to be marginally better. I seem to have seen this topic some time ago on the forums. Any suggestions before I go back to the Independent facility as I talk in lay-gibberish which they probably find difficult to understand!
Ray

[joejag308]

Bobtail, after chatting around with a few more members we cant understand the full meaning of your problem......do you mean accelerating out of the corner i would not have thought you accelerated into a corner? ....that would put the engine under load and if you get it with that then it could be an electrical fault (misfire under load) this would give a sort of a flat spot what you would also get from a fuel shortage.......it could be all sorts of different problems it cant be an accelerator cable problem as they don't have an accelerator cable.
This cable that you say cured the problem initially which cable was it.
It cant be a clutch cable with an automatic........until the facts are there we cant assume it is any certain type of fault.
Does the engine kick down when you press the accelerator all the way down?...........it is an automatic gearbox isnt it?
Sorry i cant be of any help really, but its hard to pinpoint faults when the full facts are not there......Joe

[bobtail264]

Thanks Joe
Sorry I was unclear - I did say I spoke in lay-gibberish!
Of course, one slows down approaching the roundabout and after checking all is clear, one accelerates slightly to enter the roundabout - the car increases speed slightly but with a jerk. Similarly in slowing down for traffic ahead, pedestrians or any other reasons, when you depress the accelerator pedal slightly to regain speed, it does so not smoothly but with a slight jerk.

Yes the 'kick-down' works. I believe the cable (or lead) referred to by the Independent Jaguar Facility was an electric cable. It was the contacts they cleaned.

I think it probably is the type of electrical fault you mentioned. But I do seem to remember seeing some postings or comments about this 'jerkiness' probably around the time I bought the car 17 odd months ago. I am still delighted with the car - it has now done only about 27,000 miles although first registered March 2001.

I never depress the accelerator pedal harshly, always gently, but it doesn't seem to make any difference.
Thanks
bobtail

[bobtail264]

Joe,
Sorry, yes it is an automatic.
Bobtail

[joejag308]

BOB Clean the MAF sensor with Halfords Electrical Contact Cleaner see if that works......it has been a problem smilar to yours in the past.....its going to be trial and error with this type of problem....but if it does work let us know....Joe

[Brakebuster]

good advice there from Joe,

you could also try taking off the induction pipe from the top of the throttle body ,only two 8mm bolts and the spring clips on the airbox..... this is the same pipe with the MAF sensor in it, be sure not to touch the wires when cleaning the MAF sensor , as they are a calibrated distance to detect the amount of airflow , inspect the whole tube for splits, as this will have the same effect as a bad sensor...

under the air duct the TB might well be dirty, this can be caused by the oil breather pipe at the top of the right bank going into the air duct, this adds some lubrication and hot gasses to the airflow, but it can deposit on the butterfly flap in the TB, this will be easily seen as its all black and sticky, use the same electrical cleaner and a clean cloth to remove the gunk from the butterfly, the butterfly can also be gently prised open and wedged with the soft handle of a screwdriver to allow the cleaning of the underside, but dont force it past is natural stop

when putting the induction tube on, check again for any splits, as this will bypass all the sensors and throw out the readings, and ensure the rubber seat on the TB is correctly fitted

after the air intake system, your most likley clprit will be old gearbox oil, but thats another story.....

BB

[bobtail264]

Thanks Joe Jag & Brakebuster.

Will certainly have those suggestions tried. As I say it's not a huge prob but irritating - the Volvo is smoother than the Jag which should be a contradiction in terms! The Jag is my pride and joy and is better in every conceivable respect except for jerky. Thanks again.
Bobtail

[dhammond]

I had this problem a while back which was cured by disconnecting the battery for one minute and then reconnecting (effectively rebooting the ECUs).

Note: Make sure that you know the radio code before trying this.

Regards,

David

[bobtail264]

Davis many thanks. Will try that. Still a little annoyingly jerky at the moment but then my mechanical no how not good
Ray

[bobtail264]

David. Sorry about misspelling your name. My typing's not so hot either!
Ray