Idle rising and falling

[Phid]

Got the M50 running - sounds sweet and smooth but when warm idle is rising and falling, I put the wipers on and when I turned them off it temporarily settled. So maybe an earth? Or could it be a sensor - o2?

[Phid]

Further info. The rhythmic rise and fall of revs only happens once the engine reaches temperature. If I disconnect the MAF it has no effect. If I disconnect the O2 sensor the engine idles smoothly. Is it as simple as this sensor is buggered?

Also, the M50 loom has an Evap sensor terminal. On the assumption that the car and original fuse box does not have air con I have just left this terminal. Could this be contributing? Do I need to plug something into it?

Thanks

[Phid]

Just reading up on the Evap sensor. Nothing to do with the aircon. So guess this could potentially be causing my problem. Will have a search around tomorrow night.

[Phid]

In case anyone looks back at this - it is now solved. Combination of a vacuum leak and 4 year old fuel!

[Corasdad]

Glad you got it sorted