Jerk when decelerating

LeFrog · Post by **LeFrog** » 25 Aug 2004, 15:29

Tried posting about this problem before, but thought it was engine mounts, so didn't get an overwhelming response to the subject.
If I'm in 1st, 2nd or 3rd gear (worse in 2nd) and doing about 3,000rpms and lift of the throttle completely and quickly, the car jerks as if its over engine braking. Also, when you decelerate at low speed, (say coming out of your driveway), it's nearly impossible to decelerate gently without some jerking/juddering.
Most people seem to have problems with accelerating, not decelerating.
It's starting to drive me [}:)] now, so am hoping somebody has come across this before.

Mosser · Post by **Mosser** » 25 Aug 2004, 15:43

My 1.8i 16v Xantia does exactly the same, i thought it ws normal though ?
I have noticed there is a ball on the top of the throttle butterfly and am going to try fitting a hydraulic throttle damper to see if this gets rid of it, i think it will

Stuart McB · Post by **Stuart McB** » 25 Aug 2004, 16:06

Sorry for this but on having my very first Xsara I found that the gas pedal was a little twichy, very sensitive. It seems ok but there wasn't a lot of slack in the throttle cable. Have you checked that the throttle is returning back to it full position. Just check that the throttle butterfly and all the attched bits are free and clean. My butterfly was covered in crap etc so gave it a good clean.

LeFrog · Post by **LeFrog** » 26 Aug 2004, 01:50

Checking the tension of the throttle cable and cleaning the throttle body opening was the first thing I did. Unfortunately no difference. Logic tells me it's an Oxygen, MAP or throttle position sensor. However, other people in this forum that have replaced these parts have had different symptoms.
The car only has 30,000 miles on the clock, so it shouldn't be a major thing.

JamesQB · Post by **JamesQB** » 26 Aug 2004, 18:28

Hi,
Had this problem on our Xantia 1.8 16V 1996. It used to really annoy me as well, especially in queues of traffic where I looked like a learner kangaroo-hopping. Exactly the symptoms you've described in all the same circumstances.
I managed to cure it, although a failing idle stepper motor brought back similar symptoms after a couple of weeks or so. Anyway, for the first two weeks it was like driving a new car, deceleration was smooth as could be in all gears from all speeds.
The cure was accidental, as I was trying to cure the idle stepper motor since it was causing the car to stall repeatedly. I discovered, after removing the stepper motor, that the inside of the throttle housing where it located was full of gunk, as was the stepper valve itself.
I decided to completely remove the throttle housing, strip, clean and re-build it. I also cleaned (although should have replaced) the idle motor. I took a lot of time to make the throttle housing like new and I think that's at least partly what cured the jerkiness. Also some pipes which pushed on to the housing were filled with dried oil which I cleaned out.
Hope this is of some use.
James

tomsheppard · Post by **tomsheppard** » 26 Aug 2004, 18:56

Worth checking every rubber hose thoroughly for splits and leaks where they join to their fittings. Once they have perished a little, then air gets in and the engine runs lean. Lifting off is the worst case for this because the injection has already leaned off the mixture so the fire can go out momentarily.

LeFrog · Post by **LeFrog** » 27 Aug 2004, 06:35

Well I think I have cured it and coincidently, see James' response suggesting the problem.
I mentioned before that I had given the throttle body and stepper motor a clean. For some reason, I decided to do it again, except this time, I told it who was boss. I gave it a good spray in all visible holes and even squirted some cleaner through the hoses that connect to the throttle body. I also squirted some WD40 into the stepper motor. It is much better now although I'm not sure if its the clean or the WD40 in the stepper motor that did it.
There is still some jerk, but I don't think it's far off what you would expect with a manual car. No doubt a professional dismantle and clean would completely cure it.
It seems that so much can be gained from cleaning the throttle body, yet it's never on a service schedule. Citroen ruled it out as the car had done so few miles.
Thanks to those that replied. My advice - clean your throttle body at the weekend!