fast idle and surge in motor

[662593]

I have a 91 vn executive it has started to idle high 1000-1100 rpms and when travelling about 100kphs and you take your foot off the accellerator the enging sounds like it is surging.
The motor starts fine idles fine hot or cold and it is using more petrol than normal.
I replaced the oxogen sensor about December 09 along with plugs and leads.
any idea's how to fix the problem

[Vlad01]

vacuum leak I recon.

[662593]

thanks for the info will check vacuum lines

[662593]

vacuum lines all ok

[Vlad01]

ok might be the IAC? also check that the butterfly fully closes at idle.

[mischa]

Mine done this when one of my throtle body gaskets was leaking hence letting more air into the inlet manifold after the butterfly/IAC.

[gimmemud]

Does it sound right when idling? Had the same problem after i changed the spark plugs on mine but could notice a miss. Had a brand new spark plug with a little tiny crack in it which i didn't realise until after about the tenth time staring at it at night and seeing the spark going out the side