LEH82

gets really erratic goes from 500rpm to 1500rpm or so and keeps bouncing back and forth...are these bad blow off valves or our car can not run on blow valves. put my polished diverter valves back on and no problems...i've seen many other s4's with blow off valves....

Marx

use diverter valves.

KOpork

This is car is designed to use bypass valves or DVs. It will run like crap unless you change them.

visintainer [vis]

The S4 uses a "suck-through" MAF. The DV's are located after the MAF, therefore the air passing through them is metered. If you replace them with BOV's, which vent to atmosphere instead of recirculating, you will be venting metered air and the car will run rich.

BOV's work fine on cars where the MAF is located after the BOV.


Ok, there's still some misinformation here.

First, just because a car has a MAF doesn't mean you can't use a BOV. It's the location of the MAF that matters.

Second, there is no possible way that replacing a post-MAF DV with a BOV will not result in the car running rich, even if only for a moment. The SSQ may remain closed at idle, which should help the idle problem, but when it opens it's still venting metered air.

TwentyValveB5+S4

****. replace them.

SIMPPLY @ WMS

I run blow Offs with no issues ;p ( looks around and runs like a dog )

TwentyValveB5+S4

You are evil. Well, Wicked, I suppose.

StevenH

Or do a simple search to learn they wont work with your car. You have not seen S4's running them with no problems.

S4NIC8

since the silver polished DV's run fine, I'm betting you need to polish the BOV's too

daves4izzle::ASP 3-

The first three words in your post are the root of the problem...