[s-cars] S4 Emissions Failure/also Bypass Valves

[Kaklikian, Gary]

After giving my car the best tune-up it's ever had, replacing the throttle switch unnecessarily,  and even swapping ECU's with a stock one in a futile attempt to pass emissions,  we found the problem --- a vacuum leak. Yes, obvious, but not so obvious. There were no symptoms like hard starting or rough idle typically caused by vacuum leaks, only a slight stumble and high hydrocarbons off closed throttle.

I had checked all hoses/clamps, sprayed carburetor cleaner on all fittings, etc, and then a  fellow S4 car owner says "let's pull the bypass valve." Sure enough, when removing the hose to the intercooler, the pipe on the bypass valve came off in the hose!  It was simply pressed/glued into the pos aftermarket valve from TAP (ok, my mistake). This is the latest generation valve they sell (think they call it the "group A"),  but I don't know who the manufacturer is.

Fitted a stock Bosch bypass valve and the car now passes emissions by a wide margin, even with hollow kitties!

RE: bypass valves - the Forge valve on my other car works well and appears to be higher quality than any other aftermarket ones I've used.

Thanks for all the advice on this problem.

Gary
'92 S4
'89 951