Hello, I'm hoping you guys might be able to give me some advice on my issue. My 1999 2wd Ranger 2.5l blew a head gasket, the engine had nearly 200,000 miles and other issues so I opted for a replacement engine. I got one from usa parts online but the engine looked rough, I was told that it had been run tested and I didn't want to deal with the hassle of returning it so I went with it. I put new rings on the pistons and replaced all of the gaskets, all of the internals looked fine so I wasn't worried. Upon starting it the engine ran rough, there was no smoke or blow by. I double checked the timing, spark, and fuel. It shakes harshly at idle, when giving it gas the engine will still shake but less so. If I let off the throttle quickly it will die instantly. I unplugged the MAF while idling and the shaking remained, so I bought a cheap unit off of amazon and installed it, there was no difference. I used the original wiring harness and I didn't notice any issues with it. Could the cheap MAF have been defective out of the box? What else could be the issue? Is there something I may have done wrong? Any input would be appreciated.