get on audisrs, sadly the rs4 section doesn't get too much attention here
but from what i have learnt you need to consider the following.......
Clutch - when was it last changed,, if it's older than 50k there's a chance it'll need doing during your ownership, that's be £1,000
Tyres - much life left, a good set will cost you £200 a corner
Brakes - pads and discs for the front will set you back £700, and about £500 for the rears
Dump valves - ever been changed? if they haven't there's a strong chance they are not working correctly, these will cost £40 each
EGT sensors - have these been changed? at 120,000 they could well be on their way out, so the newer the better, these cost about £180 each
Lambda sensors - not a common problem, but there's 3 of them and they cost around £300 each so if they have been changed at some time that's a bonus
MAF - like all vag cars, the mafs do go faulty, make sure it's been changed at least once during it's life, most RS4's have gone through one in their life, these cost about £180
Gearbox - 1/10 tries to get the gearbox into first or reverse when stationary often gets blocked, this is pretty normal on these and VERY common, a little gas or simply knocking the car into second instead before selecting first or reverse helps - again, this only happens in 1 out of 10 tries, probably even less, sometimes just holding the clutch down for a bit before selecting gears helps too, if that, however, there were recalls unrelated to this, 1 2 3 and 6 syncros were changed on mine by audi
Engine - pretty solid, however, some have had cam issues, i suggest you get them checked for wear, but to be honest at 120,000 miles i think you'll be fine, it's more the lower mileage cars that people worry about, however, getting them changed can cost around £2,000 !!
Thermostat - makes sure it has been changed, make sure the car heats up very quickly and after a drive, it;s only a £19 part, but it can take around 5 hours to replace !!!
Radio - bad reception can be caused by a loose areial above the amp in the rear left side compartment
Turbo's - make sure there are no leaks or odd sounds, i'm no expert, but changing these on an rs4 can create a bill way over £2,000
Suspension - check all the springs for cracks , more the rears than the front
that seems to be what i have picked up from my experience, power delivery should be very smooth, nothing like a mapped 1.8t, power should continue to increase until the red line, if you find it;s brutal low down and looses power higher up, chances are it has been mapped........ like i said, get on the srs site, maybe even give one of them a little dosh to come and go over it with you, they know their stuff
