idling problem

[frank mellin]

I have a 1999 passat 1800 with 64,000 genuine miles.Auto.
It developed a fault when idling with the revcounter swinging between 500-1500rpm.Garage have cleaned the throttle body and checked everything possible.Nothing coming up on diagnostics.Car runs beautifully but when slowing to a stop the revs still drop back to below 500rpm which results in the anti stall device kicking in .this then causes fluctuations in idle speed which for an auto is bad news!!
Surely someone has the answer................please

[cazyp]

Has the garage (really) checked:

All vacuum pipes - all the 3mm ones esp' at hose junctions and all other intake hose junctions for leaks. Intake pipes for blockages. Replace the vac lines with silicone pipe. A vac leak will cause your problem.

MAF fault? Unplug to see if there is a difference.

Coil packs - known 1.8 fault - usually on later models so I've read.

All the above will cause rough idle/dipping although my money will be on a vac leak somewhere..