Apparently I'm now "the Ford guy" at work, just because, combined, we own four Mustangs. My boss acquired a '97 F150 with a 4.6L 2V engine that might have a couple dead cylinders. He took it to his friend at a Chevy dealership, who replaced the coils and told him, "It needs a new engine." The original engine was running so rough that it felt like it had a broken con rod. We didn't dig into the old engine to diagnose it, however we did uncover some issues, such as the PCV hose from the DS VC to TB not being connected. The truck and a replacement engine, from a salvage yard (with a 3 year warranty), show up at my shop. My son and I swapped the engine and performed the following: New plugs New gaskets - oil pan, valve covers, and intake Oil/filter Water pump All new hoses New fuel filter New air filter. The condition of the new engine looks pretty good, based on inspecting the cams, spark plugs, and pulling the oil pan. After firing the new engine, it idles rough and acts like it wants to stall. It doesn't run anywhere near as bad as the original. I replaced the MAF sensor and IAC valve. The running fuel pressure is 34 PSI. The running fuel pressure increases about 5 PSI when I pull the vacuum line off the fuel pressure regulator, so I did not replace the regulator or pump. I did not replace the O2 sensors or cats. Any suggestions are greatly appreciated. I don't want to just keep throwing money and parts at it. Thanks in advance.