I have just purchased a vw fox and it's a little rough on tick over. Sometimes the engine starts to judder slightly as though it's gonna start to stall and when you push the accelerator it misses a little at the low revs before running better at slightly higher revs. I have changed the plugs, leads, coil pack, fuel filter but this has made no difference. I also cleaned the throttle body. I'm starting to run out of ideas if anyone can help ? I thought it was a misfire but I'm not so sure now. There are also no warning lights