Thanks for quick reply and yeh the car is completely standard
Its two quite significant dips and a couple people said they saw the wheel kinda jumping up and down. Guy doing the run originally thought it was something to do with the traction control but when it was turned off the
problem remained.
I had the tyre changed a couple days before but forgot about balancing the wheels so could this give such a significant dip?
Maybe something to do with the ball joint of driveshaft?
a loss of traction would defo give you a dip (or spike on a digital dyno), could be caused by various things, on my last rr star performance thought my clutch was slipping, but it turned out they were spraying the cooling water onto the front d side wheel by accident
i dont think wheel balance would cause it though, easy to tell if the wheel balance is way out just gradually acclerate up to motorway speed in a staight line and feel for the steering wheel wiggling, if you get wiggle the balance is out, but im not sure that would cause it to slip, easy way to find out is have them checked/balanced and rr it again.
what i would do first though is find a big empty road, drive with the car in 3rd at 1500 rpm, turn the tc off and floor it up to max revs, see if you can feel any dips, i can feel mine at exactelly the revs indicated on my dyno.
if the road is dry and your tyres are warm you shouldnt lose traction, and you will be able to feel the difference between a power dip/traction loss anyway (traction the revs will shoot up/steering go light).
if its traction have a garage check out the drive shaft and all that general area (this is done during MOT if thats anytime soon/recent)
if its power then you need to find out why, did the garage you went to check the ecu for fault codes? if not get it read, if anyone on the forum near you has a vagcom they will prob do it for you if you ask nice/beer tokens.
it still sounds a lot like what happened when my MAF went, but this should show up as a fault code anyway so if you find out its a defo power dip, then a reading is probably a sensible next step