Mysterious Fault after service

[Hebshelp]

Hi guys
I'm hoping someone might be able to offer some help on a mysterious fault that has appeared on my 2007 Pathfinder following service and MOT, the garage has no idea and are saying that Nissan have seen this before.

Car went in for service and MOT last Tuesday, no problems before it went in so was expecting nothing untoward. Picked the car up from the garage Tuesday evening, drove it home (about 500m from garage) and parked it on the driveway. Went out on Wednesday, started the vehicle fine, left it running to pop back into the house and noticed a nice rainbow pattern over the driveway. Can't locate a leak or tell what it is so call the garage, they come out and confirm they can't find a leak or identify what it is either. He asks me to start the car, started fine but then the engine "surges" (his words, not mine). It didn't sound like it was accelerating wildly, more a slight increase before decreasing to what I would consider normal before running ok again, the car then repeats this. They take the vehicle back to the garage and that was the last I've seen of it.

It is not a Nissan dealership as we live on a Scottish island but they say they are talking to Nissan. Over the last week, they've said it is something they've done while tinkering for the service, to a faulty ecu to a leaking hose. They also said the fault clears itself after 5-10 minutes so when the vehicle is warm. They are now saying they've found a fault of the throttle running at only 84% when idle and that the vehicle will stall from it. The throttle value is moving freely so they were hoping last night that an ecu reset would sort it out, heard nothing so rang them this morning and it hasn't worked, the car still has the fault. They are saying that Nissan have never heard of this fault before so we're currently all in limbo.

Any ideas?

[smj999smj]

If they disconnected the battery, they could have erased the idle air volume setting, which could cause it to have a rough idle or surge. If this is the case, and idle air volume relearn would be required. The easiest way to do this is with a CONSULT III scantool, or capable generic scantool, as there are several conditions that must be in range in order for it to complete. It is possible to do this without a scantool, but it can sometimes be difficult. The procedure is listed in the factory service manual, which can be downloaded at various sites on the web.
The "rainbow" is an indication of oil. It's possible that there is a leak, but it could just be just residual oil left on the skidplate that wasn't cleaned off.