Shortest version possible here: A month ago, I hydrolocked my motor. I was able to get all the water out, changed oil twice since, changed plugs, and it ran better than ever for about 2 weeks. Someone told me that I might have actually cleaned out some carbon deposits, and this could be the reason. I had it checked out just in case, and verified nothing was broken/bent, and that all sensors were doing AOK. Then just about a week ago, my car began to sputter for a second every time I started it up, I lost all kinds of torque (it hardly wants to move without stalling in any gear below 3k RPMs), and it smelled like exhaust when I was moving forward slowly. I took off the headsheild (stock exhaust, 99 GS), and noticed that my stock exhaust manifold was cracked, in the same place I’ve heard a lot of 2GNTers complain about. For grins, I’ve ordered the Greddy 4:1 header and PS cat-back exhaust (since my muffler has lots of tiny holes in it, anyways), but I somehow doubt this will fix anything when it arrives. Sometimes, when I’m trying to get going in first, it’ll even pop (sounds like a backfire?) if I’m taking off without giving it tons more throttle than I’m used to. Even though I'm conscious of this problem and nursing it now, I'll still occaisionally almost stall it now trying to get going. It seems to run decent though any time in any gear as long as I'm above 3k RPMs or so. The gas mileage is also taking a major turn for the worse. I used to get ~ 330 mi to a tank whereas now I’m lucky to get 220. I’ve changed plugs again, and all seems fine with the old ones. It idles OK, but when I'm sitting in neutral and I give it just a bit of gas, it sputters before it revs again. I checked out the spark wells, and there is no oil leakage (new valve cover gasket and rings just about 6 months ago. I have no idea what could be causing this, but it almost seems to be worsening. My only thought after everything I’ve checked is that perhaps the crack on the exhaust manifold is causing a bad reading to the O2 sensor @ the down pipe, and this is perhaps sending bad data to the ECU causing it to run like crap. But I kinda doubt this as it's just a small crack, and have heard several guys tell me they've had this before with no performance differences noticed. Can anyone tell me why I’m experiencing this huge loss in torque and general crappy performance? Thanks always for all your help.