I was driving my car the other afternoon ('03 RS6 in the US) and took it out for a back roads blast and then a couple mile hit on the highway...decided to air it out a bit up to a good clip since there was a clear open stretch of highway to 140 or so and immediately gave a light brake to slow back down. I noticed a pretty significant shudder in the front end that felt like a severely warped rotor. This kept up for about another mile off of the highway and then disappeared at lower speeds. Over the weekend (about a week later without driving the car), my son and I headed to the Audi USA cars & coffee in VA about 60 miles away...after 30-40 miles, we noticed a pretty strong shudder again when braking for toll booths (car was driven at normal highway speeds, nothing excessive). On the way home from the event, it got pretty severe and made me a bit worried that something could possibly be loose as it felt like it was right in the driver's front wheel...further down the road, still on the highway, it went away. One other funky note still on the same trip home is that when taking a sweeping highway overpass/onramp at 50-60, when coming back towards the straight, the ESP light started flashing and lost power right when I was getting ready to merge with light acceleration when coming out of the curve...this went off quickly though, but definitely affected the acceleration when the ESP was flashing.

A few thoughts...I just installed new springs and struts that drop the car about 1.5". The car is running with a nubcake stage 2 tune (love it!) and a TCU tune.

My first inclination is maybe a wheel speed sensor, any thoughts or input? Reason for the suspension replacement was a leaking DRC line that hit the driver's front wheel with a fair bit of oil and was worried a bit about oil on the brake pads, so maybe another suspect, but shouldn't cause the ESP light, just maybe a braking shudder.

One final note, I took it for a short ride yesterday and ran it up to 100 or so...braked perfectly fine just as expected...no shudder at all.

Any input is appreciated!