I was just recently wheeling and sunk the front end of the engine down fairly good enough to stall it since the fan was paddling water all over the top of the engine. After I got it out it was louder than before, muffler fell off and cat wasn't tightened down fully. Now the truck has a low idle and it lopes up and down but doesn't like to stay idling. If I let up off the gas it'll drop to around a 400rpm bouncing up to 700rpm idle and after a couple cycles just stall out. I'm thinking maybe when I was getting pulled out the passenger side manifold got cracked or loose possibly? I haven't looked at it just yet since I have to clean off the engine to get a good look but the manifold is my thought. When I was restarting the truck it was flashing the CEL really fast constantly until I hit the gas then it would throw code 51, I'd try to start and it'd go back to flashing really fast. Now with it running the CEL isn't coming on at all but its still loud and has the idle problem. Any ideas?

 

o2 sensor or vacuum line, hmm that is strange.