jerky on/off throttle xantia 2.0 16v

[bikemad650]

Here goes,If i'm traveling in traffic at a constant speed for example and i lift off the throttle the car doesn't slow for about a second as if the throttle is still on.Then it comes off quite jerky and not very smooth.It's similar to letting the throttle off in an automatic car where you have no engine breaking.The throttle doesn't seem to be sticking ar all under the bonnet,I't doesn't do it all the time though and is sometimes smooth.Its a P reg 2.0 16v xantia if that helps,starts and runs perfect otherwise, Any suggestions appreciated. thanks