Au Surging

[BF MKII UTE]

I have an AU1 I6 auto, tickford intake, k&n filter, headers, hi flo cat and 2 1/2" system and an unopened engine with 135,000klm.
Serviced regulary, had an EFI tune done about 7000k's ago involving plugs,fuel filter, K&N cleaned and reoiled, fault codes checked (all clear).

It has recently started to surge when running at a steady speed at running temperture. I can be sitting on 60km/h or 80 and it will intermittently surge forward in revs and off then surge again.

I have had it in my local trusted Ultra Tune and they did all the checks again, come up with some fault codes that pointed to the MAP sensor, i had them replace it and then codes cleared.

Car ran well for 2 weeks and now tonight problem has returned

Has anyone got any ideas what could be causing this ? :

I have also always used the same premium unleaded from the same servo for the past 5 years with no problems.

Thanking you in advance
Alan.