Need Help With Throbbing Idle

[cruisermark]

my mark 4 when fully warmed has a thumping/throbbing type idle

warm idle is about 600 rpm - I know my previous lexs used to idle around this figure

it is mostly noticeable when sitting in the driving seat and appears to be coming from under the car directly below rather than engine based - it does goes away if the revs are slightly raised to about 800.

the car had a new starter put on before I bought it - could something have been not put right properly??

any pointers welcome

[Bluesbreaker]

Difficult to diagnose without actually hearing it,but if it's a 'throbbing' noise, coming from underneath you, could be exaust, but that wouldn't diminish if you took the revs up any higher, -it would get worse, could be something loose though, vibrating at idle speed, but stopping as revs are increased, sorry I can't be any more specific.

[black400]

Is it a trob or rattle, ? trob oxegene sensor, trottle body or senor, rattle loose engine cover / engine mount but unlikely, also engine underlay?