Help please! Mercedes w220 s class airmatic super-stiff damping!

Mark Benjamin • 9 October 2019

Greetings all, from the UK. Can anyone help please?

The Airmatic damping on my immaculate treasured W220 'S' is super-stiff at all 4 corners (front to rear, side to side and diagonally).  The car runs on standard 17" alloys with OE 225/55 x 17 Continental tyres at the correct pressures with no mods to the suspension, but even low speed minor road ruts and ridges send severe jolts through the cabin as if the entire system is permanently locked into 'safe' (stiff) mode and not releasing / adjusting pressure to the struts according to the conditions. My best analogy is that the car rides (or rather bounces!) over even minor road imperfections like a skateboard.  

History: well maintained car, Airmatic compressor and relay replaced at 60k miles, 2 x recent 'STAR' diagnostics not showing any fault codes, suspension does not lose height when parked up (so leaks not suspected), maintains correct ride height always.  Dashboard switch raises / lowers height correctly, but Sport 1 & 2 settings are inoperative although the lights come on. No wiring faults found on recent physical examination, no Airmatic warnings on dash, so I'm completely baffled.

My Question: could the problem be due to a faulty / seized valve block (but which for some reason is NOT showing any codes?).  Or, similarly, the pressure relief (release) valve in the compressor?   So far, 2 Merc Indies here in the UK haven't solved the problem.  All they say is: "the struts actuate ok and we can't see any fault codes on STAR, thank you and goodbye".  Mmmm...

All thoughts, advice and experiences welcomed to restore the 'magic carpet' ride that the S Class is famous for - many thanks!

Mark B.