So it starts with the O2 sensor. I had a relatively new single wire, it was acting this way so I bought a new three wire, and it too is doing this. It reads normal with the key on and the engine off, around 500. I start the car, and it steadily drops to 0. If I hit the gas, as soon as I let off it reads up to 800 and then quickly down to 0 again. So the sensors is working, correct? This is definitely an exhaust leak, no?

The trouble is, if it's a leak it's obviously drawing air IN, causing a false lean. Now I used Seafoam to realize the collector gaskets needed tightening because it was blowing OUT, but how do I find a leak if it's sucking IN? I've got brand new gaskets all around, soft thick aluminum collector gaskets and marine gaskets on the head side. I have a feeling these headers are a terrible match, is there a fool proof gasket I could try? I'm so close to having this engine running like new, it's just this one damn bug...

Or am I totally off and it's something else entirely?

 

Just to further illustrate my situation, these are most likely Flowtech headers. They were on the car when I bought it and I found Flowtech stickers in the center console so I think it's safe to assume. After reading others' opinions of Flowtech, I guess I shouldn't be surprised I have a leak. Again. Any ideas on making them work for now? Assuming my O2 sensor is indeed screaming "leak!"