Acv???

[Cobra_R]

Whats an ACV, what does it do and do you need it, cuz iv seen people remove it and wondered why.

[theflatlander]

ACV-air control valve. This is on the lower intake manifold, and the air pump feeds air into it. The ACV controls where the air pump's air goes - into the main cat, into the exhaust manifold, or into the silencer that's under the passenger side headlight. The '89-91 NA's have their 6-ports and VDI actuated from air pump pressure, so the ACV is required unless you fab something up. Oh yeah on a S4 fc it is not needed. but if you remove it you can also take the air pump out but you'll also need a duel belt pulley for your alternator so that your water pump functions correctly.

[Cobra_R]

what would be the benefits of taking the ACV and air pump out?

[theflatlander]

less stuff to deal with in the engine bay.